^. 


IMAGE  EVALUATION 
TEST  TARGET  (MT-S) 


^. 


4 


./ 


^< 


^ 


^ 


« 


1.0 


1.1 


25 
2.2 


■a  12.8 

US  Itt 

u  HA 

Sf   U£    12.0 


lai  111^  IJ-^ 


I 


FhotograiJiic 

^Sciences 

Corporation 


r<N- 


s> 


23  WIST  MAIN  STREET 

WE»STER,N.Y.  145M 

( 71* )  •72-4503 


4R> 


i 


CIHM/ICMH 

Microfiche 

Series. 


CIHIM/iCIVIH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historical  Microraproductions  /  Institut  Canadian  da  microraproductions  historiquas 


/• 


Tachnieal  and  Bibliographic  NotM/Not«s  taoliniquM  at  iiibliographiquat 


Th« 
tot 


Tha  Inatituta  liaa  attamptad  to  obtain  tha  baat 
original  copy  availabia  for  filming.  Faaturaa  of  thia 
copy  wlilch  may  ba  bibliographlcally  unlqua, 
which  may  altar  any  of  tha  imagaa  in  tha 
raproductlon,  or  which  may  aignificantly  changa 
tha  uaual  mathod  of  filming,  ara  chacicad  balow. 


D 


D 


D 
D 


D 


D 


Colourad  covara/ 
Couvartura  da  coulaur 


r~1   Covara  damagad/ 


Couvartura  andommagAa 

Covara  raatorad  and/or  laminatad/ 
Couvartura  raataurAa  at/ou  pallicuMa 


I     I   Covar  titia  miaaing/ 


La  titra  da  couvartura  manqua 

Colourad  mapa/ 

Cartaa  gAographiquaa  an  coulaur 

Colourad  ink  (i.a.  othar  than  blua  or  black)/ 
Encra  da  coulaur  (i.a.  autra  qua  blaua  ou  noira) 


r~n   Colourad  plataa  and/or  illuatrationa/ 


Planchaa  at/ou  illuatrationa  an  coulaur 


Bound  with  othar  matarlal/ 
Raiii  avac  d'autraa  documanta 


Tight  binding  may  csiuaa  ahadowa  or  diatortlon 
along  intarior  margin/ 

La  re  iiura  sarrte  paut  cauaar  da  I'ombra  ou  da  la 
diatortlon  la  long  da  la  marga  intiriaura 

Blank  laavaa  addad  during  ras'ioratlon  may 
appaar  within  tha  taxt.  Whanavar  poaaibla.  thaaa 
hava  baan  omittad  from  filming/ 
II  aa  paut  qua  cartainaa  pagaa  blanchaa  ajouttoa 
lora  d'una  raatauration  apparalaaant  dana  la  taxta, 
mala,  loraqua  cala  Atalt  poaaibla,  caa  pagaa  n'ont 
paa  4tA  fiimtea. 

Additional  commanta:/ 
Commantairaa  aupplAmantairaa: 


L'Inatitut  a  microfi.-ni  la  malllaur  axamplaira 
qu'ii  lui  a  At*  poaaibla  69  aa  procurar.  Laa  dAtaiia 
da  cat  axamplaira  qui  aont  paut<Atra  uniquaa  du 
point  da  vua  bibllographiqua,  qui  pauvant  modlfiar 
una  imaga  raproduita,  ou  qui  pauvant  axigar  una 
nvodification  dana  la  m^thoda  normala  da  filmaga 
aont  indiquAa  ci«daaaoua. 


Th< 


D 
D 
D 
[2 
D 
0 
D 
D 

n 


Colourad  pagaa/ 
Pagaa  da  coulaur 

Pagaa  damagad/ 
Pagaa  andommagAaa 

Pagaa  raatorad  and/or  laminatad/ 
Pagaa  raatauriaa  at/ou  palilculAaa 

Pagaa  diacolourad,  atainad  or  foxad/ 
Pagaa  dteolortea,  tachattoa  ou  piqutea 

Pagaa  datachad/ 
Pagaa  d^tachAaa 

Showthrough/ 
Tranaparanca 

Quality  of  print  variaa/ 
Quality  inAgala  da  I'impraaaion 

Includaa  aupplamantary  matarlal/ 
Comprand  du  matirial  auppMmantaIra 

Only  adMon  availabia/ 
Saula  Mitlon  diaponibia 

Pagaa  wholly  or  partially  obacurad  by  arrata 
allpa,  tiaauaa,  ate,  hava  baan  rafilmad  to 
anaura  tha  baat  poaaibla  imaga/ 
Laa  pagaa  totalamant  ou  partiallamant 
obacurciaa  par  un  fauillat  d'arrata,  una  palura, 
ate,  ont  At*  fllmAaa  A  nouvaau  da  fa9on  A 
obtanir  la  malllaura  imaga  poaaibla. 


oft 
filn 


Ori 
baf 
tha 
atoi 
oth 
fira 
aioi 
ori 


TN 
aha 

TIN 


Ma 
diff 
ant 
bag 

rigl 
raqi 
mat 


Thia  Itam  la  filmad  at  tha  reduction  ratio  chackad  balow/ 

Ca  doeumant  aat  filmA  au  taux  da  rAductlon  indiquA  ci-daaaoua 

10X                          14X                     .     18X                          22X 

28X 

30X 

y 

n 

12X 

16X 

aox 

24X 

2SX 

32X 

I 

itails 
idu 
odiffiar 
'un« 


Th«  copy  filmed  hw  hat  bean  raiiroduead  thanka 
to  tha  ganaroalty  of: 

Broek  Unhrtnity 
StCathiriiMf 

Tha  imagaa  appaaring  hara  ara  tiM  baat  qualltv 
poaaibia  oonaidaring  tha  condition  and  laglbiiity 
of  tha  original  copy  and  in  kaaping  with  tho 
filming  contraet  apaeif ieationa. 


Original  eoplaa  in  printad  papar  covara  ara  fllmad 
beginning  with  tha  front  oovar  and  andlng  on 
tha  iaat  paga  with  a  printad  or  illuatratad  impraa- 
aton,  or  tha  back  eovar  whan  appropriate.  AS! 
othar  originji  copiaa  ara  fllmad  beginning  on  the 
firat  puge  with  a  printad  or  illuatrated  impree- 
aion.  and  ending  on  the  Iaat  page  with  a  printed 
or  illuarrated  impreealon. 


L'a«amplaira  filmi  fut  reproduit  grice  i  la 
gAnAroaitA  da: 

Broek  UnKrartity 
St  CitharinM 

Lea  imegea  suivantaa  ont  Ati  raproduitea  avac  la 
piua  grand  soin,  compta  tanu  da  la  condition  at 
da  la  nettetA  de  raxampieire  film*,  at  an 
conf  ormM  avoc  lea  conditiona  du  contrat  da 
fllmage. 

Lea  axempleirea  originaux  dent  la  couvartura  an 
papier  eat  imprim^e  sent  filmto  an  commandant 
par  la  premier  plot  et  en  terminent  aoit  par  Ic 
darnlAre  pege  qui  somporte  une  amprainta 
d'Impreaaion  ou  d'iiiuatration,  aoit  par  la  second 
plot,  selon  le  cea.  Toua  lea  autrea  axempleirea 
originaux  sent  film4a  en  commen^ant  par  la 
pramlAre  pege  qui  comporte  une  empreinte 
d'Impreaaion  ou  d'illuatration  et  en  terminent  per 
le  demlAre  page  qui  comporte  une  telle 
empreinte. 


The  leet  recorded  freme  on  eeeh  microfiche 
ahaM  contain  the  symbol  «^(meening  "CON- 
TINUED"), or  the  symbol  ▼  (meening  "END"), 
whichever  appliee. 


Un  dee  aymbolee  suiventa  appareltra  sur  la 
damiAre  imege  de  cheque  microfiche,  selon  le 
caa:  la  symbole  ^  signifle  "A  SUiVRE".  le 
symbole  y  signifle  "FIN". 


Maps,  platea,  charta.  etc..  mey  be  filmed  et 
different  reduction  retioa.  Thoae  too  ierge  to  be 
entirely  included  in  one  expoaure  ere  filmed 
beginning  in  the  upper  left  hend  comer,  left  to 
right  and  top  to  bottom,  aa  many  framea  aa 
required.  The  following  diegrema  illuatrate  the 
method: 


Lea  cartea.  planchea,  tableaux,  etc.,  pauvent  Atra 
filmAa  i  dea  taux  de  rMuction  diffArenta. 
Loraque  la  document  eat  trop  grand  pour  Atra 
reproduit  en  un  seul  clichA.  il  est  fiimA  A  partir 
de  Tangle  supArieur  gauche,  de  qeuche  A  droite, 
et  de  haut  mn  bee,  en  primant  le  nombre 
d'Imegee  nAceaaaire.  Lea  diagremr.tea  suiventa 
Uluatrant  le  mAthode. 


rrata 
to 


pelure, 
nA 


□ 

32X 


1 

2 

3 

1 

2 

3 

4 

5 

6 

REPORT 


ON  riiK 


RENEWAL 


OP 


NIAGARA  SUSPENSION  BRIDGE. 


BY 


LEFFERT    L.   BUCK, 


CIVIL   ENGINEER. 


xeso. 


NEW  YORK: 
C.  W.  Ames  &  Co.,  Pkintkks,  96  Chamukks  Stukict. 

1881. 


145245 


Names  (if  memhcrs  of  the  Boards  of  Directors  of  the 
Niagara  Falls  Suspension  and  Niap:ara  Falls  International 
riridp^e  Companies  during-  the  progress  of  the  work  : 

^iiiei'traii  )Bom;b. 

Hon.  r,OKK\Z()  hi  KKOWS.  I'iun. 


AI-MKUT  S.  WAKXKR,  Sk(  kktvuv. 

Hon.   I{.  L.  BURIKIWS. 

UKU.   I,.  BIKROWS. 

Col.  V.  A.  ROKBLINfJ. 

A.  STKWART. 

C.  n.   MOORK, 


JOSEPH  A.  AVOODRUFF,  I'kks. 
J.  F.  McGLASIIAN,  SEc.iKTAiiv. 
Hon.  J.  R.  BENSON. 
THOMAS  R.  MERRITT. 
Right  Rev.  T.  B.  FULl  ER 
RICFIARD  MILLER. 
JOHN  L.  RANNKY. 


WILLIAM  (..   SWAN,  Superintauknt. 


To  the  Presidents  and  Gentlemen  of  the  Hoards 
of  Directors  of  the  Niagara  Falls  Supension  and  the 
Niagara  Falls  International  Bridge  Companies: 


Gkntlemen: 

Having  completed  the  work  of  rein- 
forcing the  Anchorage  and  renewing  the  Suspended 
Superstructure  of  your  bridge,  I  respectfully  submit 
the  following  report. 

LFFFFRT   L.   lUXK. 

December  13th,  1880. 


I 


REPORT 

ON  THE  REINFORCEMENT  OF  THE  ANCHORAGE  AID  RENEWAT, 
OF  THE  SUSPENDED  SUPERSTRUCTURE  OF  THE  NIAGARA 
RAILROAD  SUSPENSION   BRIIKJE. 

From  the  inception  of  the  project  of  spanning  the  chasm  of 
the  Niagara  River  below  the  Falls,  with  a  siisj)ension  bridge 
for  railroad  puri)oses,  to  the  year  1855,  when  the  bridge  was 
completed  and  opened  to  traffic,  it  was  considered  bj  all  as  a 
bold  undertaking  and  by  some  engineers,  even,  as  an  impracti- 
cable one.  But  tlie  bridge  has  been  in  constant  use  for  twenty- 
five  years  and  under  constantly  increjising  traffic,  thus  demon- 
strating its  adaptability  to  a  locality  requiring  such  long  spans. 

In  spite  of  its  succe>^s,  however,  it  has  been  an  object  of 
constant  solicitude  to  the  traveling  public.  The  frightful 
chasm  that  it  spans  would  naturally  excite  the  fears  of  most 
people,  but  this  has  been  greatly  enhanced  by  doubts  as  to  tlie 
condition  of  the  cables  and  their  anchorage. 

The  object  of  this  Eeport  is  to  show  what  the  real  condition 
of  the  cables  and  anchorage  was,  and  also  to  indicate  what  has 
been  done  ior  their  improvement,  as  well  as  that  of  other  parts 
of  the  bridge. 

In  order  to  explain  this  clearly,  it  is  necessary  to  insert  here 
the  following  general  description  of  the  structure  as  it  was. 


DESCRIPTION. 

The  bridge  consisted  of  the  following  members :  " 

1st.  Two  pairs  of  iron  wire  cables  resting  on  masonry  towers 
at  each  end  of  the  bridge.  The  ends  of  the  cables  are  secured 
by  means  of  chains  to  suitable  cast  iron  anchor  plates  bedded 
in  the  rock  forming  each  bank  of  the  river.  Two  of  these 
cables  have,  at  mean  temperature,  a  versedsine  of  54  feet,  and 
are  designated  upper  cables.  The  other  pair  having  a  versed 
sine  of  64  feet,  are  called  the  lower  cables. 


6 

2(1.  Tlie  Suspended  Siiperatructure. 

Tliis  consisted  of  two  floors,  placed  at  a  vertical  distance 
apjiit  of  17  feet  and  co!inocted  by  posts  and  rods  in  such  a 
man  nor  as  to  form  a  trussed  tube. 

At  each  five  feet  in  the  length  of  the  trusses,  two  wire  rope 
suspenders  connect  the  up{)er  floor  with  the  uj)per  cables.  In 
the  Slime  manner  the  lower  floor  is  suspended  to  the  lower 
cables. 

CONSTRUCTION  OF  THE  CABLES. 

Each  cable  is  composed  of  seven  strands  or  bundles  of  wire. 
Each  strand  is  made  up  of  520  scant  No.  9  wires  laid  })arallel, 
and  at  each  end  formed  into  a  loop  which  fits  into  a  groove  in 
a  U  shaped  cast  iron  shoe.  The  seven  strands  are  bound  into 
one  bundle,  of  3,640  wires,  which  is  served  closely  with  wire 
over  the  whole  length,  with  the  exception  of  about  13  feet,  at 
each  end,  and  of  about  10  feet  of  the  portions  resting  on 
the  towers,  thus  forming  a  cylindrical  cable  \0^  inches  in 
diameter. 

The  tops  of  the  towers  are  each  covered  with  a  cast  iron 
plate,  8  feet  square,  bedded  in  mortar.  The  upper  surface  of 
this  plate  is  planed  to  a  true  surface.  On  it  rest  a  number  of 
turned  iron  rollers  5  inches  in  diameter.  On  these  rollers  rest 
the  saddles,  consisting  of  heavy  castings,  whose  undersides  are 
planed.  The  top  of  each  saddle  has  a  groove  of  semi-circular 
section  in  which  the  wires  of  the  cable  lie,  each  cable  having  a 
separate  saddle.  The  planes  of  the  curves  of  the  cables, 
between  the  towers,  are  inclined  in  such  a  manner  as  to  bring 
those  of  each  pair  nearer  together  at  the  middle  of  the  span,  to 
give  lateral  stability  to  the  bridge.  From  the  towers  to  the 
anchorage  the  cables  diverge  from  the  center  line  of  the  bridge 
sufRciently  to  make  the  platie,  containing  the  portion  each 
side  of  the  tower,  vertical.  The  wire  forming  the  cables  was 
boiled  in  linseed  oil  before  it  was  laid,  and  as  the  cables 
were  made  the  interstices  at  the  shoes  and  towers  were  flushed 
with  boiled  linseed  oil  and  Spanish  brown  paint.  Then  the 
whole  length  of  the  cable  was  flushed  with  the  same  as  the 
serving  progressed. 


ti 


i 


ANCHOR AUK 

Each  end  of  each  cable  lias  a  separate  ancliornge  tlie  derfcrip- 
tion  of  wliich  will  be  assisted  by  referring  to  Plate  1. 

A  rectangular  pit  or  shaft,  3  ft.  x  7  ft.  in  plan,  was  snnk 
vertically  into  tlie  rock,  to  a  deptii  of  25  feet,  with  the  bottom 
enlarged  to  form  a  chamber  7  ft.  square.  An  anchor  phite, 
6  ft.  6  in.  stpiare  and  having  seven  rectangular  opetiings  tlirongh 
it  to  receive  the  lower  links  of  the  anchor  cluiin,  is  set  in  the 
chamber,  the  links  put  in  position  and  secured  by  a  8.1  inch 
diameter  pin  passed  through  their  heads  and  underneath  the 
plate.  From  the  plate  the  chain  passes  vertically  upward  to 
the  surface  of  the  rock.  From  this  point  the  joints  of  the 
chain  are  at  points  of  a  vertical  curve  of  25  ft.  radius.  The 
joint  at  the  upper  end  of  the  curve  lorming  the  j)oint  of 
tangency  with  the  line  of  the  cable.  Beyond  this  joint  is 
another  length  of  chain  composed  of  nine  links,  each  bar  of 
which  is  10  feet  long  and  7  in.  x  If  in.  section.  Four  of  these 
links  alternate  with  the  shoes  of  three  of  the  strands  of  the 
cable  and  are  secured  to  them  by  a  3^  in.  diameter  pin  passing 
through  links  and  shoes.  The  remaining  five  links  are  in  like 
manner  connected  with  the  remaining  four  shoes  of  the  cable 
strands,  as  shown  in  elevations  (Fig.s.  1  and  2). 

The  anchor  plates  are  secured  in  tlie  chambers  by  means  of 
neatly  fitted  stone  blocks  set  in  cement  mortar,  the  whole  pit 
being  solidly  filled  with  cement  masonry  and  the  interstices 
around  the  bars  grouted.  Above  the  rock  and  np  to  the  end 
of  the  chain  the  whole  is  enclosed  in  a  solid  wall  of  masonry, 
heavy  blocks  of  which  form  supports  of  the  joints  of  the 
curved  portion  of  the  chain.  Formerly  the  strands  were  also 
covered  with  masonry  and  the  whole  grouted,  the  intention 
being  to  preserve  them  from  corrosion. 


CONSTRUCTION  OF  THE  OLD  SUSPENDED 
SUPERSTRUCTURE. 

As  first  built  the  superstructure  was  as  follows  (see  right 
hand  half  of  transverse  view  and  side  elevation  of  old  truss, 
plate  IV.) 


8 


1st  A  aeries  of  transverse  bents,  one  at  eacli  five  feet  in  tlie 
length  of  the  bridge,  or  161  in  nil.  Kucli  bent  consisted  of  the 
following  parts: 

a.  Lower  floor  beam.  This  was  made  of  two  pieces  of  4  in. 
X  1()  in.  pine  timber,  24  feet  long,  set  on  edge,  parallel  and 
with  a  6  in.  space  between  them. 

b.  Two  posts.  Kach  post  was  composed  of  two  pieces  of 
4  in.  X  0  in.  pine  placed  parallel  and  separated  4^  inches  by 
packing  blocks.  The  lower  ends  of  the  posts  were  secured  l)e- 
tween  the  two  parts  of,  and  (lush  with,  the  lower  edge  of  the 
lower  floor  beam.  The  clear  distance  between  the  posts  of  a 
bent  was  19  feet. 

c.  U{)per  floor  beam.  The  upper  beam  was  the  same  as  the 
lower,  exc(;pt  that  it  was  26  feet  long.  The  top  of  the  post 
was  flush  with  the  top  of  the  beam  and  clamped  between  its 
two  parts. 

d.  Knee  braces.  Each  bent  ^as  stiffened  transversely  by  a 
4  in.  X  6  in.  pine  knee  brace  from  the  under  side  of  the  upper 
beam  to  the  inner  face  of  the  post. 

2d.  Longitudinal  members. 

a.  Upper  and  lower  chords. 

The  upper  chords  each  consisted  of  two  thicknesses  of 
2  in.  X  12  in.  white  oak  plank  in  lengths  of  5  feet,  the  joints  of 
one  thickness  being  at  the  middle  of  the  lengths  of  the  other. 
They  were  bcHed  together  with  eight  ^  in.  bolts  to  each  length. 
These  chords  laid  on  tops  of  posts  and  beams. 

The  lower  chords  were  each  made  of  three  thicknesses:  one 
of  pine  2^  in.  x  12  in.,  one  of  pine  4  in.  by  12  in.,  and  one  of 
oak  2  in.  x  12  in.,  all  in  6  feet  lengths  and  bolted  together  with 
eight  ^  in.  bolts  to  each  panel.  The  lower  chords  were  laid  under- 
neath the  ends  of  the  posts  and  the  undei*sides  of  the  lower 
floor  beams. 

b.  Track  Stringers. 

There  were  two  deep  longitudinal  track  stringers  built 
partly  above  and  partly  below  the  upper  floor  beams.  The 
portion  above  the  floor  beams  was  made  of  4  in.  x  16  in.  pine 
planks  piled  closely,  broadsides  horizontal  and  to  a  height 
above  the  beams  of  2  ft.  6in.     The  rails  for  the  track  were 


ect  in  the 
ted  of  the 

s  of  4  in. 
allel  and 

pieces  of 
iiches  by 
3ured  he- 
re of  tlie 
of  a 


3 

JStS 


le  as  the 
the  post 
ween  its 

e]y  by  a 
e  upper 


3sses  of 
joints  of 
e  other. 
I  length. 

ses:  one 
one  of 
er  with 
i  under- 
e  lower 


3  built 
I.  The 
n.  pine 
height 
£  were 


i 


laid  on  the  tops  of  thcso  shIiilmth.  Tlic  portion  ol  cjich 
stringer  below  the  bcjMiis  wiis  nuidr  <»1  two  picfCH  of  pine 
tiniber,  one  piece  being  12  in.  \  12  in.  and  the  otlier  12  in.  x 
10  i»i.  Thev  W(!re  \\\m\o  eoiitinuoiis  by  searle*)  and  keyed 
spliceH.  The  spaces  between  the  upper  iiiid  lower  portions  ol 
the  stringers  and  from  t)nc  beiini  to  anoliier  were  tilled  by 
bridging  pieces  4  in.  tliicU.  There  were  5  long  ])olts  (1  itich 
diameter)  to  eacii  panel  lenglli  ol  stringer  extending  llirongh 
from  top  to  i)ottoni. 

c.  Ilarnl  rails.  At  each  side  of  the  npper  lloor  was  a  iieavy. 
trussed  lian<l  rail,  exteiidin^r  iho  whole  length  of  the  ])ridge. 
At  each  beam  a  \l  in.  diameter  bolt  passed  Irom  the  top  ol  tiie 
hand  rail  down  between  the  pjirts  of  the  beam  mid  ihroujih  an 
8  in.  X  9  in  loiii^itinlinal  pine  string  piece.  This  string  piece 
was  made  continuous  ])y  splicing. 

d.  Upper  lloor.  Tlu;  planking  of  the  upper  lloor  was  laid 
lengthwise  and  fastened  to  tlic  beams  by  means  of  screws. 
The  |)t)rtion  between  tlie  track  stringers  was  of  4  in.  j)lank, 
the  renniinder  was  2  in.  thick. 

c.  Lower  lloor  planking.  The  first  course  of  ])1atdc  was  of 
pine  2  in.  thick.  The  top  course  of  oak  2  in,  thick.  Both 
courses  were  laid  lengthwise  an«l  secuied  to  the  beams  with 
scrcw.s. 

/  Cornices.  To  the  ends  of  the  ujipcr  ami  lower  floor  beams 
were  secured  strong  cornices. 

3d.  Truss  rods.  The  truss  rods  were  at  first  made  of  1  in. 
diameter  round  iron  with  a  nut  on  each  end.  Tliev  extended 
each  way  from  the  bottom  ol  each  jiost  diagonally  to  the  top 
of  the  fourth  post  distant,  passing  lhron<jh  the  chords  and 
secured  by  the  nuts  being  screwed  down  to  the  face  of  a  cast- 
iron  angle  washer. 

4th.  Susj)enders.  The  lower  cable  suspenders  were  attached 
by  means  of  stirrup  to  the  ends  of  the  lower  floor  beams. 

Those  of  the  upper  cables  were  attached  to  the  upper  floor 
beam  on  each  side,  about  midway  between  the  track  and  the 
trusses. 

5th.  Stays. 

a.  From  the  top  of  each  tower,  where  one  end  of  each  was 


■ 


(i 


10 

secured  to  the  saddle,  sixteen  wire  rope  stays  extended  to 
various  points  of  the  upper  and  lower  floors.  They  were  of 
wire  rope  4^  in.  circumference.  The  longest  reached  to  a 
point  250  feet  from  the  end  of  the  truss. 

b.  Attached  to  each  side  of  the  lower  floor,  at  intervals  of  25 
feet  for  the  whole  length  of  the  bridge,  excepting  75  feet  at 
each  end,  were  wind  stays  whose  other  ends  were  fastened  to 
the  ro'^ks  on  each  side  of  the  river.  There  are  fifty -six  of  them 
in  all. 

CHANGES  IN  TEE  OLD  WORK. 

After  the  bridge  had  been  in  use  for  some  time,  it  was  found 
that  the  lower  floor  did  not  assist  the  chords  until  the  latter 
had  been  overstrained,  after  which  the  constant  working  of  the 
joints  at  the  intersection  of  posts  with  bf;ams  and  chords,  had 
produced  rapid  decay  of  these  parts.  As  they  became  weak- 
ened and  the  stress  came  upon  the  floor  planking,  the  screws 
holding  them  to  the  beams  were  loosened,  allowing  moisture  to 
get  in  aid  causing  the  upper  edges  of  the  beams  to  rot. 

To  remedy  this  difficulty,  auxiliary  chords,  composed  of 
heavy  timber,  were  bolted  to  the  undersides  of  the  lower  floor 
beams,  parallel  with,  and  just  inside  of  the  truss  rod  chords. 

To  obviate  the  necessity  of  removing  the  old  beams,  their 
projecting  ends  were  cut  off,  the  posts  were  cut  off  level  with 
the  tops  of  the  beams,  the  portion  between  the  beams  removed, 
and  pieces  of  6  in.  x  13  in.  pine  timber  inserted  from  each 
side  of  the  bridge,  their  inner  ends  meeting  at  the  center  line 
and  their  outer  ends  projecting  to  form  an  attachment  for  the 
lower  suspenders  and  to  which  the  lower  cornices  were  attached. 
The  lower  ends  of  the  posts  then  rested  upon  the  new  bejims 
and  oak  shoulder-blocks  were  spiked  to  the  sides  of  beam  and 
post.  The  bolts  holding  the  auxiliary  chords  passed  up 
through  these  new  beams  and  remaining  portions  of  the  old 
beams  (between  which  the  new  ones  were  placed)  were  secured 
by  bolts  passing  through  all  three. 

Such  was  substantially  the  arrangement  of  the  parts  of  the 
bridge  up  to  the  year  1877.  But  the  upper  floor  had  been 
renewed  in  1873,  though  no  alteration  was  made  in  the 
arrangement. 


11 

When  in  the  condition  above  described,  the  whole  suspended 
weight,  between  the  towers,  including  cables,  stays  andsus- 
penders,  was  estimated  at  1,180  tons. 


INSPECTION. 

In  the  latter  part  of  February,  1877,  Mr.  Thomas  C.  Clark,  of 
the  Phoenixville  Bridge  Co.,  with  a  view  to  examining  the  con- 
dition of  the  portions  of  the  cable  strands  embedded  in  the 
masonry,  caused  a  small  excavation  to  be  made  near  one  of  the 
shoes.  On  reaching  the  first  strand,  two  or  three  of  the  wires 
were  found  to  be  corroded  quite  through  and  others  were 
partially  corroded. 

Shortly  afterward  Col.  W.  H.  Paine,  of  the  East  River 
bridge,  visited  the  bridge  and  gave  orders  for  the  removal  of 
all  the  masonry  covering  the  strands  of  each  cable.  He  also 
made  tests  of  the  elongation  of  the  strand  portion  of  one  of 
the  cables,  by  means  of  a  vernier  scale.  He  found  in  this 
way  that  the  elongation  under  a  given  moving  load,  on  the 
bridge,  was  no  greater  than  the  modulus  of  the  wires  would 
allow,  supposing  the  total  section  to  be  the  same  as  when  the 
cables  were  new.  He  also  cut  out  some  pieces  of  wire  and 
tested  them  for  tensile  strength,  ductility,  &c. 

Their  ultimate  strength  was  fully  equal  to  that  of  the  new 
wire  per  unit  of  section,  and  their  reduction  of  ruptured 
section  was  satisfactory,  but  as  the  wires  tested  were  etched  in 
places,  of  couise  the  stretch  would  be  principally  confined  to 
the  etched  portion,  hence  rendering  any  measurement  of  the 
stretch  a  matter  of  extreme  diificulty. 

On  the  16tli  of  March,  1877,  the  writer  joined  Col.  Paine  at 
Suspension  Bridge  to  assist  in  examining  the  condition  of  the 
bridge  and  in  repairing  the  defective  wires. 

After  the  strands  were  thoroughly  cleaned  and  the  wire 
bands  removed,  they  were  opened,  the  paint  removed  from  the 
interstices  and  the  inner  wires  examined.  They  were  found  to 
be  in  as  good  condition  as  when  first  put  in. 

The  outer  defective  wires  were  cut  away  so  as  to  uncover 
the  second  layer  of  wire  at  the  bend  of  the  shoe,  when  the 
second   layer,  or  course,  was  found  to  be  sound  and  bright. 


12 


Thus  it  was  found  that  the  only  wires  affected  were  the  outer 
wires  of  the  outside  strands.  Near  the  cylindrical  portion  of 
the  cables,  the  outer  wires  were  slightly  rusted  clear  around  the 
cable,  but  as  we  approached  the  shoes,  the  etching  appeared  to 
work  toward  the  lower  strands,  till,  when  the  shoes  were 
reached,  the  principal  corrosion  was  of  the  outer  wires  under- 
neath the  bottom  shoes. 

The  evident  cause  of  this  corrosion  was  the  elongation  and 
contraction  of  the  strands  under  the  passing  loads,  which  had 
loosened  the  cement  from  the  outside  strands,  allowing  moisture 
to  work  in  and  finally  reach  the  lowest  point.  The  portion  of 
cement  among  the  strands  would  go  and  come  in  a  body  with 
the;n. 

Occasionally  a  limestone  spawl  had  been  carelessly  left  in 
contact  with  a  strand,  when  they  were  being  covered,  in  which 
case  the  contact  was  indicated  by  a  black  spot.  On  cleaning 
this  away  the  wires  immediately  under  it  were  found  to 
be  corroded  partly  through  the  outer  layer. 

While  the  examination  was  going  on,  the  defective  wires 
were  cut  out  and  new  ones  spliced  in  under  strain.  The 
greatest  number  of  wires  that  required  repairing  at  one  end  of 
any  one  cable  was  sixty-five. 

On  the  29tli  of  March,  1877,  Messrs.  Milnor  W.  Eoberts,  T. 
E.  Sickles  and  Col.  W.  H.  Puine  visited  the  bridge,  at  the  re- 
quest of  the  Board  of  Directors,  and  made  an  examination  of 
the  cables,  both  at  the  strands  and  at  the  saddles.  These  gen- 
tlemen reported  that,  in  their  opinion,  as  soon  as  the  repairs, 
then  going  on,  were  completed,  the  cables  would  be  in  good 
condition. 

A  copy  of  their  report  was  sent  to  the  G.  W.  R  y  Co.,  whose 
only  reply  was  to  call  for  a  Commission  of  engineers  to  make 
an  examination  of  the  bridge  and  report  upon  its  condition 
according  to  the  terms  of  their  contract. 

The  Bridge  Companies  then  selected  Col.  Paine,  the  G.  W. 
R'y  Co.  chose  Mr.  Thomas  C.  Clark,  find  these  two  gentlemen 
gelected  Mr.  Charles  Macdonald.  The  Commission  arrived 
April  17th.  During  that  and  the  three  following  days,  they 
aiade  a  very  thorough  examination  of  the  bridge  and  all 
portions  of  the  anchorage  that  were  accessible. 


tmmm 


13 


ibe  outer 
artion  of 
ound  the 
pea red  to 
jes  were 
IS  iinder- 

tion  and 
hieh  had 
noisture 
)rtion  of 
>dy  with 

y  left  in 
n  which 
sleaning 
>und   to 

e  wires 
1.  The 
J  end  of 

lerts,  T. 
the  le- 
ition  of 
se  gen- 
repairs, 
n  good 

,  whose 
•  make 
idition 

G.  W. 

tlemen 
irrived 
3,  they 
ad   all 


Very  particular  attention  was  paid  to  the  condition  of  the 
anchor  chains.  Measurements  of  the  sections  of  all  the  upper 
lengths  of  bars  in  each  chain  were  taken,  and  of  the  siaes  of 
heads  and  pins  of  the  same,  showing  the  following  conditions: 

1st.  The  outer  bars  of  each  set  had  a  rather  greater  section 
than  the  intermediate  ones,  and  the  total  section  of  the  bodies 
of  the  nine  links  of  a  chain  was  86.626  square  inches,  the 
average  width  of  each  bar  being  7  inches,  and  the  thickness  If 
inches. 

2d.  The  diameter  of  the  pin  was  found  to  be  scant  3^  inches, 
or  hardly  five-tenths  of  the  width  of  the  body  of  the  bar.  The 
form  of  the  eye  bar  head  was  approximately  circular,  with  a 
diameter  of  about  12  inches.  The  ceuicrs  of  the  pin  holes 
were  distant  from  the  centers  of  the  heads,  and  toward  the 
body,  so  far  that  in  some  instances  the  minimum  section  on 
each  side  of  the  eye  was  less  than  half  that  of  the  body  of 
the  bar. 

3d.  Some  of  the  pins  through  the  shoes  were  found  to  be 
bent  convex  toward  the  cable  5-16  inch  in  their  total  bearing 
lengths. 

4th.  Two  or  three  of  the  pin  holes  were  open,  back  of  the 
pin,  nearly  ^  inch,  while  at  each  side  of  the  pin  they  were  close 
down,  showing  the  holes  to  be  eliptical.  This  was  probably 
caused  by  the  hole  having  been  bored  a  little  too  large,  which 
allowed  them  to  elongate,  or  the  bars  may  not  have  been  quite 
long  enough.  At  the  close  of  the  inspection  a  test  load  of 
nearly  450  tons,  composed  of  a  switch  engine  and  twenty 
loaded  box  cars,  was  run  upon  the  bridge  and  points  of  the 
curves  of  undulation  taken  with  a  level  for  each  position  of  the 
load,  at  stations  100  feet  apart. 

The  bridge  regained  its  original  camber  when  the  load  passed 
off.  The  Commission  also  made  many  tests  of  specimen  wires 
cut  from  the  strands. 

After  due  consideration  the  Commission  reported  substan- 
tially as  follows: 

That  the  repairs  of  wires,  affected  by  rust,  having  been  com- 
pleted, the  action  of  the  wire  portion  of  the  cables  indicated 
that  they  were  in  good  condition. 

But  regarding  the  anchor  chains,  it  was  believed  that  the 


1^ 

form  of  the  heads  and  size  of  the  pins  would  not  enable  these 
parts  to  transmit  a  greater  ultimate  strain  upon  the  bodies  of 
the  links  than  40,000  lbs.  per  square  inch  of  their  total  section. 
Consequently  while  each  of  the  cables  possessed  an  ultimate 
strength  of  3,640  x  1648=5,998,720  lbs.,  or  say  6,000,000  lbs., 
the  chain  would  not  probably  sustain  a  greater  strain  than 
86.625  X  40,000=3,465,000  lbs.  or  6,000,000—3,465,000= 
2,535,000  lbs.  less  than  the  cable.  The  section  of  new  chain 
necessary  to  supply  the  deficiency,  estimated  at  50,000  lbs.  per 
square  inch  would  consequently  be  50.7  square  inches. 

The  report  was  accompanied  with  plans  for  this  reinforce- 
ment and  required  that  it  should  be  made. 

The  report  also  suggested  the  renewal  of  the  suspended 
superstructure  with  iron,  and  submitted  a  general  plan  lor  that 
purpose. 

REINFORCEMENT  OF  THE  ANCHORAGE. 

The  plans  accompanying  the  Commission's  report  were  pre- 
pared from  data  obtained  from  Mr.  Roebling's  published  report 
on  Niagara  Suspension  Bridge.  It  proposed  the  sinking  of 
one  new  pit  into  the  rock  at  the  back  end  of  each  anchor  wall, 
with  a  chamber  at  the  bottom  for  the  reception  of  three  small 
anchor  plates.  To  the  middle  plate  were  to  be  attached  two 
chains  which  were  to  pass  vertically  upward  to  the  surface  of 
the  rock  and  thence  to  follow  a  curve  till  they  became  tangent 
to  the  line  of  the  upper  cable,  and  thence  to  pass  one  on  each 
side  of  the  old  chain  and  attach  to  the  strands  of  the  cables.  This 
connection  was  to  be  formed  as  follows:  (see  plate  I.)  Into 
each  shoe  was  to  be  fitted  a  cast  iron  block  with  one  end  con- 
cave to  fit  against  the  pin.  There  were  seven  of  these  blocks 
at  each  end  of  a  cable.  The  outer  ends  of  all  these  blocks  to 
be  dressed  off"  in  the  same  plane  at  right  angles  to  the  center 
line  of  the  cable  at  this  point.  Two  cross  bars,  with  a  side  of 
each  planed,  were  to  rest  against  the  cast  iron  blocks  and  have 
their  ends  turned  for  the  upper  ends  of  the  new  chains  to  take 
hold  of 

Each  of  the  other  two  chains  were  to  be  made  fast  to  one  of 
the  outer  plates,  and  passing  upward,  in  a  curve,  till  tangent  to 


,r 


15 

the  line  of  the  lower  cable,  and  thence  passing  up,  one  each  side 
of  the  old  wall,  to  attach  to  the  lower  cable  in  the  same  man- 
ner as  in  the  case  of  the  upper  cable  chain. 

The  strains  were  to  be  applied  by  leaving  one  of  the  joints 
of  each  chain,  on  the  curve,  about  two  inches  nearer  the  center 
of  curvature,  than  any  of  the  others  and  having  the  chain  in 
this  position  just  the  right  length  to  allow  of  connecting  to  the 
cable,  then  expand  the  chains  by  heat  and  as  they  lengthened 
raise  the  low  joint  and  block  it  with  iron  plates,  after  which  the 
cooling  of  the  chain  would  cause  it  to  contract  and  thus  relieve 
the  old  chain  of  a  portion  of  its  load. 

MEASURExMENT  OF  STR^  'NS. 

Each  bar  of  the  upper  length  of  each  chain  was  to  be  subjected 
in  a  testing  machine  to  a  stress  equal  to  the  permanent  load  to 
come  upon  it  and  the  corresponding  elongation  noted.  The 
same  elongation  to  be  given  to  them  when  in  position. 


EXECUTION  OF  THE  WORK. 

The  plan  above  described  was  to  be  subject  to  such  altera- 
tions as  circumstances  should  require. 

I  was  selected  as  engineer  in  charge  of  the  reinforcement  and 
arrived  at  Suspension  Bridge  September  13th,  1877,  and  com- 
menced at  once  the  removal  of  the  earth  to  uncover  the  rock. 

On  getting  to  the  surface  of  the  rock,  it  was  found  that  the 
profiles  of  the  anchorage  given  in  the  report  of  Mr.  Roebling, 
from  a  typographical  error,  was  a  combination  of  the  profiles 
of  both  sides  of  the  river,  that  is,  that  the  wall  of  the  Canada 
anchorage  and  the  height  of  the  rock  surface  on  the  New  York 
side  were  given  in  the  same  profile.  Hence  by  placing  the  pits 
at  the  back  of  the  old  wall  in  each  case,  the  line  of  the  lower 
cable,  on  the  Canada  side,  would  enter  the  rock  30  feet  away 
from  the  pit,  and  that  on  the  New  York  side  12  feet.  This 
would  require  expensive  trenches  in  the  rock,  the  cutting  of 
which  would  necessitate  blasting  nearer  to  the  old  anchor  pits 
than  would  be  safe. 

I  accordingly  made  alterations  in  the  plan  which  will  be  un- 
derstood by  referring  to  Fig  1,  Plate  I. 


16 

In  this  plan  the  pits  were  located  the  aame  as  in  tlie  other, 
but  smaller.  One  anchor  plate  in  each  pit  was  made  to  answer 
for  all  the  four  chains.  There  were  eight  links  secured  in  the 
plate  by  one  pin,  and  the  first  joint  (c)  was  secured  by  one  long 
pin.  Beyond  (c)  each  of  the  four  chains  was  independent  of 
the  others,  but  hcjd  the  same  curvature  and  rested  on  the  same 
sione  supports.  Two  of  the  chains  connected  with  the  upper 
cables.  The  other  two  passed  along  grooves  cut  in  each  side 
of  the  wall,  passmg  the  supports  of  the  old  upper  cable  chains 
and  fastened  to  the  lower  cable. 

As  will  be  seen  by  Fig.  1,  Plate  I,  the  plan  followed,  required 
a  bend  in  the  lower  cable  chain,  to  bring  it  on  to  the  line  of  the 
cable.  This  was  done  by  dividing  the  change  of  direction 
among  three  points,  and  securing  them  in  position  by  means  of 
stirrups  attached  to  the  ends  of  the  pins  of  the  old  chain,  as 
shown  at  a,  b  and  c. 

The  connection  with  the  strands  was  made  as  in  the  first 
plan,  excepting  that  instead  of  the  last  links  attaching  directly 
to  the  cross  bars,  a  triangular  link  is  interposed,  as  shown  by 
the  dotted  line  in  Fig.  2.  The  arrangement  of  the  holes  in 
this  I'nk  is  shown  in  Fig.  3.  The  object  of  the  link  is  to  cause 
a  proper  distribution  of  the  strains.  There  b^ing  three  stiands 
above  and  four  below,  three-sevenths  of  the  strain  should  go  to 
the  upper,  and  four-sevenths  to  the  lower  strands.  Hence  the 
resultant  of  the  strain  on  the  entire  chain  was  made  to  coincide 
with  the  center  line  of  the  cable  at  this  point,  e  and  J]  the 
centers  of  the  upper  and  lower  cross  bars  respectively,  are  in 
a  plane  at  right  angles  to  the  center  line  of  the  cable,  and  the 
line  joining  e  and/  is  intersected  by  the  center  line  at  a  point, 
distant  from  e,  four-sevenths  of  the  whole  distance,  a.  d,  the 
point  of  attachment  of  the  chain  to  tho  triangular  link,  is  on 
the  center  line  of  the  cable. 


APPLICATION  AND  MEASUREMENT  OF  STRAIN. 

These  were  made  as  before  described  in  the  case  of  the 
upper  cable,  but  in  that  of  the  lower  it  was  not  necessary  to 
apply  heat,  as  the  joint  at  A  could  be  raised  up  and  blocked, 
after  which  the  strain  was  effected  by  screwing  down  the  nuts 


17 

of  stirrups  a,  b  and  c  (Fig.   1)  until  the  scale  irdicated  the 
proper  elongation  of  the  eye-bars. 

The  total  section  of  new  chain  attached  to  each  cable  is  50 
inches  for  all  that  portion  above  the  curve.  From  the  upper 
end  of  the  curve  downward  it  gradually  decreases  till,  at  the 
anchor  plate,  it  becomes  40  square  inches. 


METHOD  OF  DOING  THE  WORK. 

1st.  Sinking  the  Pits. — In  plan  the  pits  are  6  ft.  x  2  ft 
6  in.  On  the  New  York  side  they  were  sunk  to  a  depth  of  17 
feet  On  the  Canada  side  to  23  feet  At  the  bottom  the  pits 
were  chambered  to  6  f t  x  7  ft  in  plan,  for  the  reception  of  the 
anchor  plates. 

In  sinking  the  pits  holes  were  first  drilled  along  the  four 
sides  of  each  as  near  together  us  the  drills  would  work 
without  running  the  holes  together,  and  to  nearly  the  full 
depth  of  the  pit  The  core  was  then  blasted  out  with  light 
charges  of  dynamite. 

The  roofs  of  the  chambers  were  dressed  true  and  bush  ham- 
mered. Just  above  the  chamber  notches  were  cut  in  the  sides 
and  ends  of  the  pit 

2d.  Anchor  Plates.— These  are  of  cast  iron  5  ft  6  in. 
square  and  strongly  ribbed.  Each  plate  has  eight  cavities 
cored  into  it  for  the  reception  of  the  lower  heads  of  the  links, 
enclosing  them  perfectly.  One  pin  passes  through  the  whole 
eight  links  and  all  the  partitions  of  the  plate.  The  upper  sur- 
face slopes  outward  and  downard  each  way  from  the  link 
openings. 

After  the  plate  was  properly  placed  in  the  pit  it  was  solidly 
concreted  underneath.  The  stone  blocks  above  the  plate  were 
cut  to  fit  each  place  with  thin  joints,  and  the  pieces  as  large  as 
could  be  got  into  the  chamber  and  notches.  All  vacant  places 
were  filled  solidly  with  stone  and  cement,  but  no  stone  was 
permitted  to  come  in  contact  with  the  chains. 

In  removing  the  portions  of  the  walls  necessary  to  place  the 
new  chains,  they  were  taken  down  nearly  to  the  positions  for 
the  beds  of  the  knuckle  supports,  after  which  the  beds  were 


18 

prepared  with  poims  and  bush  hammer  in  order  to  give  solid 
beds  and  thm  joints. 

The  work  of  cutting  the  grooves  each  aide  of  tlie  walls  for 
the  reception  of  the  lower  cable  chains  required  extreme 
caution,  especially  where  they  passed  along  the  aide  of,  and 
and  partly  under  the  ends  of,  the  stone  supports  of  the  old 
upper  cable  chains.  Tn  the  case  of  the  south  wall,  on  both 
sides  of  the  river,  these  old  supports  had  been  solidly  bedded, 
but  in  both  north  walls  we  found  large  cavities  under  two  of 
them.  In  such  cases  the  cutting  had  to  be  suspended  till 
cement  mortar  could  be  forced  under  and  have  time  to  set,  as 
of  course  the  least  settlement  of  any  of  these  supports  would 
destroy  the  adjustment  of  the  cable  if  it  did  not  endanger  the 
bridge. 

After  the  new  chains  were  adjusted  the  masonry  was  rebuilt 
and  both  new  and  old  chains  covered  and  grouted  solidly.  But 
the  wire  strands  were  covered  with  brick  houses.  Each  house 
is  provided  with  a  hatchway  in  the  roof  to  give  access  to  the 
strands  for  purposes  of  inspection  and  painting. 


I 


DURABILITY. 

Possibly  the  question  may  be  asked  :  Will  these  new  chains 
continue  to  do  their  share  of  the  work  ? 

By  referring  to  the  drawing  (Fig.l,  Plate  I)  it  will  be  seen 
that  the  only  manner  in  which  the  chains  can  become  slack,  is 
from  settlement  of  the  knuckle  supports  and  shrinkage  of  the 
joints  around  the  anchor  plates.  But  these  joints  are  all  thin 
and  the  mortar  had  become  thoroughly  set  before  the  strain 
was  applied. 

At  the  time  the  strain  was  applied,  the  sun  was  shining 
directly  upon  the  chains,  making  them  warmer  than  they  can 
possibly  become  again,  covered  with  masonry  as  they  now  are, 
and  hence  the  strain  would  naturally  increase  by  covering 
them.  Again  one  of  the  upper  cable  chains  was  left  uncovered 
from  D  to  F  and  without  any  support  at  E  for  two  weeks.  That 
joint  settled  only  half  an  inch  out  of  a  right  line  and  remained 
so  during  the  two   weeks,   notwithstanding  that  the   writer 


19 


give  solid 

walls  for 
I   extreme 
ie  of,  and 
»f  the  old 
1.  on  both 
y  bedded, 
er  two  of 
nded   till 
to  set,  as 
•ts  would 
inger  the 

IS  rebuilt 
flly.  But 
ch  house 
33  to  the 


w  chains 

be  seen 
slack,  is 
e  of  the 
all  thin 
e  strain 

shining 
hey  can 
low  are, 
overing 
covered 
s.  That 
mained 
writer 


jumped  upon  it  and  shook  it  in  order  to  overcome  the  friction 
of  the  joint 

In  concluding  this  report  on  the  anchorage,  it  is  proper  to 
speak  of  the  developments  made  by  uncovering  the  old  chains. 

From  the  condition  of  the  cement  around  the  curved  portion 
of  the  chain  it  appears  that  the  miisonry  covering  them  in  the 
wall  was  put  on  before  the  weight  of  the  bridge  came  upon 
them  As  this  weight  was  added  the  curved  portion  of  the 
chain  had  settled  forward  toward  the  river  and  downward.  This 
settlement  was  greatest  near  the  top  of  the  wall.  From  this 
point  downward  it  decreased  till  about  the  third  joint  down 
where  it  was  very  slight.  That  such  settlement  had  occurred 
was  shown  by  there  being  cavities  behind  the  chains  and  ends 
of  the  pins,  both  of  which  were  rusty,  while  in  front  of  the 
chains  and  pin  ends  the  cement  was  close,  and  when  chipped  off 
left  the  iron  bright  as  when  new. 

The  rust  was  all  scraped  off  and  the  old  chains  painted, 
after  which  they  were  re-grouted  and  c<^vered  by  the  masonry, 
so  that  no  water  can  reach  them  again. 

I  neglected  to  mention,  in  its  proper  place,  that  the  cross 
bars  resting  against  the  cast  blocks  in  the  shoes  are  of  crucible 
steel,  of  a  pretty  high  grade,  but  thoroughly  annealed.  There 
was  not  sufficient  room  between  the  strands  to  properly  place 
iron  bars  of  sufficient  size  to  afford  the  proper  strength  and 
stiffness. 

RENEWAL  OF  THE  SUSPENDED  SUPERSTRUCTURE. 

While  the  work  of  reinforcing  the  anchorage  was  in  progress, 
I  made  a  careful  study  of  the  old  superstructure,  both  to  ascer- 
tain its  condition  and  also  the  requirements  of  a  new  iron  truss 
that  would  be  adapted  to  take  its  place. 

The"  Condition  of  the  Old  Trusses. — About  they  ear 
1873,  the  upper  floor  had  been  renewed.  The  lower  had,  in 
addition  to  the  auxiliary  chords  and  slip  beams  (already  men- 
tioned), been  repaired  from  time  to  time,  new  pieces  being 
inserted,  here  ahd  there,  as  the  old  ones  had  become  decayed 
or  broken. 


r.7xsr.'?a<°.'.'a" 


20 


As  the  strain  from  the  trusses  had  to  be  transmitted  to  the 
auxiliary  chords  by  the  transverse  stiffness  of  the  floor  beams, 
the  frequent  wrenching,  to  which  these  latter  had  been  sub- 
jected, had  opened  their  tibre,  and,  from  the  action  of  water 
and  frost,  had  caused  them  to  decay  with  excessive  rapidity. 

The  old  truss  rod  chord  had  become  nearly  worthless  before 
the  auxiliary  one  could  act,  and  vfhen  the  latter  did  begin  to 
act  it  was  compelled  to  do  the  whole  work,  consequently  it  had 
already  parted  in  several  places. 

In  short,  while  it  appeared  that  by  constant  repairing  the 
structure  had  been  kept  in  safe  condition,  it  was  evident  that 
the  expense  of  keeping  it  so  must  greatly  increase,  and  that,  at 
no  very  distant  date,  it  would  become  necessary  to  renew  the 
entire  truss  system  either  in  wood  or  iron. 

Whatever  course  should  be  decided  upon,  it  was  necessary 
that  the  work  should  be  done  without  stopping  the  traffic.  To 
effect  an  entire  renewal,  with  either  wood  or  iron,  without  stop- 
ping the  traffic,  would  require  an  entire  change  from  the  old 
plan.  It  was  desirable  to  decrease  the  weight  as  much  as  pos- 
sible. To  do  so  with  timber  would  require  the  best  of  sounds 
clear  material,  which  is  every  year  becoming  more  scarce  and 
expensive.  Even  then  it  is  doubtful  whether  a  wooden 
structure,  possessing  the  requisite  strength,  could  be  made  of 
less  weight  than  the  old  one  on  account  of  the  loss  of  strength 
caused  by  cutting  away  material  to  form  splices  suitable  to 
resist  tensive  stresses.  Moreover  the  best  constructed  wooden 
structure  would  require  renewal  again  in  a  few  years. 

The  manufacture  of  iron  had  reached  a  degree  of  perfection 
that  rendered  it  a  cheap  material,  and  it  was  open  to  none  of 
the  objections  pertaining  to  wood. 


CONDITIONS  TO  WtllCH  THE  NEW  SUPERSTRUC- 
TURE MUST  BE  ADAPTED  WHEN  MADE  OF 
IRON. 


1st.  The  object  of  the  trusses  is  to  prevent  too  great  undula- 
tions of  floors  and  cables  from  the  action  of  partial  live  loads 
and  from  wind,  but  yet  it  must  not  possess  too  great  rigidity. 


liMwuwim-iMijuaiiMiajiaHi 


mm 


21 


2d.  The  cables  being  anchored  at  both  ends,  there  is,  between 
extremes  of  temperature,  a  difference  in  versed  sine  of  about 
two  feet.  The  trusses  must  be  arranged  to  accomodate  them- 
selves to  that  change  without  taxing  the  cables  too  much  in 
deflecting  them. 

8d.  If  stays  from  the  towers  to  different  points  of  the  floors 
contmue  to  be  used,  the  trusses  should  be  continuous,  and  the 
middle  point  of  their  length  should  have  as  little  movement 
endwise  as  possible  in  order  to  make  the  stays  effective  at  all 
temperatures.    The  only  use  of  the  stays  is  to  assist  the  trusses. 

The  first  of  the  above  conditions  is  met  by  giving  to  the 
trusses  a  depth  such,  that  with  the  maximum  deflection,  allow- 
able, under  a  maximum  bending  load,  the  members  will  not  be 
subjected  to  more  than  the  proper  stress  per  square  inch. 
Then  give  to  each  member  such  a  section  as  v/ill  enable  it  to 
resist  greater  deflection. 

The  second  requirement  is  satisfied  in  a  manner  similar  to 
the  first,  that  is  by  giving  the  trusses  a  depth  that  will  enable 
the  cables  to  bend  them  half  the  amonnt  of  their  change  of 
versed  sine  without  too  great  stress  upon  cables  or  truss  mem- 
bers Probably,  in  most  cases,  if  this  condition  is  satisfied,  the 
depth  will  be  found  to  be  right  for  the  first  condition. 

The  third  condition  may  be  satisfied  by  making  the  trusses 
continuous  from  end  to  end,  while  at  each  abutment  is  arranged 
some  means  for  automatically  limiting  the  movement  endwise 
to  a  given  p.mount. 

In  the  present  case  the  depth  of  truss  was  approximately 
fixed  by  that  of  the  old  structure.  But  the  depth  was  reduced 
as  much  as  possible  by  placing  the  lower  chord  on  top  of  the 
lower  floor  beams  instead  of  below  them  as  in  the  old  structure. 

While  the  work  of  reinforcing  the  anchorage  was  going  on, 
I  prepared  plans  for  renewing  the  suspended  superstructure  in 
iron.  They  received  Col.  Roebling's  approval,  and  it  was  my 
wish  to  let  the  contract  for  furnishing  the  materials  so  that  it 
could  be  delivered  during  the  fall  and  winter  of  1878-9  and  be 
ready  for  erection  in  the  following  spring.  But  the  Board  of 
Directors  was  not  ready  to  commence  upon  it  at  that  time  and 
nothing  more  was  then  done  about  it. 


•  I 


if 
i  ■ 

! 
j 

pi! 


22 

During  the  following  winter  the  question  of  using  steel  for 
the  suspended  superstructure  of  the  East  River  Bridge  came 
up  and  I  turned  my  attention  to  obtaining  what  information  I 
could  regarding  that  material,  to  determine  its  adaptability  to 
this  work.  I  here  take  occasion  to  acknowledge  my  indebted- 
ness to  Col,  W.  n.  Paine  for  many  valuable  notes  and  sug- 
gestions upon  the  use  of  steel  for  structural  purposes. 

There  appeared  to  be  no  doubt  as  to  its  being  the  best  mate- 
rial for  many  of  the  members  of  the  bridge,  provided  that  suit- 
able shapes  could  be  obtained,  as  its  great  strength  would  admit 
of  decreasing  the  dead  load  of  the  bridge  materially.  But  the 
use  of  steel  had  not  yet  reached  a  point  at  which  all  the 
required  shapes  could  be  obtained  economically. 

Consequently  I  prepared  specifications  which  would  be 
adapted  to  the  use  of  either  iron  or  steel,  or  a  combination  of 
both  materials. 

During  the  discussion  of  the  steel  question  I  submitted  my 
general  plans  to  the  members  of  the  Commission  for  their  ap- 
proval which  was  given  in  a  letter  to  the  Board  of  Directors. 

On  the  7th  of  May,  1879,  a  committee  on  construction,  ap- 
pointed by  the  Board  of  Directors,  met  at  the  bridge  office,  and 
after  discussing  the  plans  and  specifications,  authorized  me  to 
invite  lenders,  from  manufacturing  firms,  for  furnishing  the 
materials  and  erecting  the  same. 

May  28th  the  bids  were  opened  in  the  presence  of  the  Board 
and  the  contract  awarded  to  the  Pittsburgh  Bridge  Co.,  that 
company  being  the  lowest  bidder. 

By  the  specifications  and  the  terms  of  the  contract  the 
materials  were  all  to  be  delivered  at  Suspension  Bridge,  ready 
for  erection,  by  August  1st,  1879,  and  the  erection  completed 
by  November  1st,  1879. 

The  specification  gave  a  preference  to  Bessemer  steel,  made 
under  the  "  Hay  Process,"  for  the  reason  that  it  had  been  the 
material  used,  exclusively,  in  a  bridge  built  at  Glasgow,  Mo., 
by  Wm.  Suoy  Smith,  and  which  had  given  very  good  results. 
But  the  Pittsburgh  Bridge  Co.'s  tender  was  for  Bessomer  steel 
and  for  iron.  Bessemer  steel  met  the  requirements  of  the 
specifications  very  well  as  will  be  seen  by  the  following  ex- 
tract from  that  document : 


mttmummmmmm 


4^ 


?  Steel  for 
itlge  came 
)rnintion  I 
tability  to 
indebted- 
and  sug- 

■ 

Jest  mate- 
that  suit- 
uld  admit 
But  the 
ii  all  the 

^'ould    be 
ination  of 

itted  my 
their  ap- 
rectors. 
2tion,  ap- 
ffice,  and 
d  me  to 
bing  the 

le  Board 
Co.,  that 

•act  the 

,  ready 

mpleted 

1,  made 
een  the 
w,  Mo., 
results. 
ST  steel 
of  the 
iDg  ex- 


23 

QUALITY  OF  MATERIALS  REQUIRED. 

All  wrought  iron  must  be  of  a  tough,  fil)rou8  character, 
double  relined.  Burs,  of  moderate  dimensions,  must  be  capable 
of  being  bent  cold,  through  90**,  with  un  inner  diameter  of  cur- 
vature, not  ttxceeding  the  thickness  of  the  bar,  without  crack- 
ing. When  nicked  and  beut  sharply  over  the  corner  of  an 
anvil,  the  fracture  produced  must  show  a  good  clean  fibre.  It 
must  have  an  ultinmte  tensile  strength  of  at  least  60,000  lbs. 
per  scjmvre  inch  of  sectional  area,  and  an  elastic  limit  of  at  least 
25,000  lbs.  per  square  inch,  when  tested  in  specimens  turned  to 
cylindrical  form,  the  turned  portion  of  which  has  a  length  of 
at  least  ten  diameters.  It  must  elongate  at  least  15  per  cent, 
before  rupture.  The  area  of  action  at  point  of  fracture  should 
red  ice  as  nearly  26  per  cent,  of  original  area  as  possible,  in 
order  to  be  uniform  in  hardness.  A  uniform  modulous  is 
desirable. 

The  steel  must  be  of  a  quality  such,  that  in  dimensions  to 
be  used,  it  shall  have  an  ultimate  tensile  strength  of  not  less 
than  70,000  lbs.  per  square  inch  ot  section,  and  an  elastic  limit 
of  not  less  th>tn  40,000  lbs.  per  square  inch  in  tension,  or  in 
compression,  when  the  specimens  have  a  moderate  length  com- 
pared to  their  diameters. 

Specimens  bent  cold  through  90®,  with  an  inner  diameter  of 
curvature  not  greater  than  one  and  a  half  diameters  of  the  bar, 
must  not  show  any  cracks  or  flaws.  When  the  specimens  are 
tested  in  tension,  with  a  strain  of  40,000  lbs.  per  square  inch  of 
section,  their  power  for  resisting  shocks  may  be  tested  by 
striking  them  smartly  with  a  hammer  while  under  that  strain, 
when  they  must  not  crack. 

The  specimens  must  elongate  at  least  ten  per  cent,  of  their 
original  length  before  rupture,  and  their  ruptured  sections  must 
be  reduced  at  least  twenty  per  cent,  of  their  original  sections. 
Uniformity  in  modulus  and  ductility  is  to  be  secured  as  far  as 
possible. 

On  reaching  Pittsburgh  I  made  some  tests  of  specimens  of 
Bessemer  steel.  They  gave  very  good  results  ;  but  the  only 
shapes  to  be  obtained  in  steel  were  plates,  angles  and  small 
channels. 


H 


24 


I  then  decided  to  use  steel  for  the  posts,  chords,  track  string- 
era  a"d  lateral  rods.     All  other  parts  to  be  of  iron. 

As  the  chords  must  be  constructed  of  plat3s  and  angles 
riveted  together,  the  net  section  would  necessarily  be  reduced 
to  a  greater  extent  than  if  channels  were  used,  on  account  of 
the  greater  number  of  rivet  holes  required,  hence  there  could 
be  no  great  advantage  in  point  of  weight  by  using  steel,  unless 
of  a  higher  quality  than  that  called  for  by  the  specifications. 

I  then  found  at  what  increase  of  price  per  lb.  the  Hay  steel, 
with  an  ultimate  strength  of  80,000  lbs.  and  elastic  limit  of 
48,000  lbs.,  could  be  obtained  and  decided  to  use  that  material 
for  the  chords. 


PROGRESS  OF  THE  MANUFACTURE. 


,::i 

N 


Immediately  after  the  contract  had  been  awarded  for  furnish- 
ing this  material,  there  started  up  a  demand  for  iron  and  steel 
that  was  unprecedented.  The  mills,  throughout  the  country, 
had  more  orders  than  they  could  fill.  Consequently  when  the 
time  arrived,  at  which  the  materials  should  have  been  delivered 
at  the  bridge,  the  work  at  the  shops  had  scarcely  commenced,  and 
very  little  of  the  raw  materials  had  come  from  the  mills.  It 
soon  became  evident  that  nothing  could  be  done  about  erection 
during  the  fall  of  1879,  However  the  work  generally  went 
forward  in  the  shop  when  there  was  sufficient  material  on  hand 
to  work  to  advantage. 

Every  precaution  was  taken  to  do  the  work  in  a  satisfactory 
manner. 

Tests  were  made  upon  specimens  cut  from  every  blow,  and 
then  from  specimens  cut  from  the  actual  shapes  from  each  blow 
for  all  the  steel  used,  and  with  no  other  preparation.  (See 
appendix.) 

In  building  the  chords,  the  angles  were  first  laid  out  for 
punching.  Tue.  holes  were  punched  about  ^  iixoh  too  small. 
They  were  then  clamped  to  the  plates,  in  proper  position,  and 
a  drill  of  proper  size  passed  through  both  angle  and  plate,  the 
angle  being  thus  reamed  and  at  same  time  serving  as  a  templet 
for  drilling  the  plate.     This  prevented  any  possibility  of  one 


mm 


25 

part  bringing  any  stress  upon  another,  as  the  holes  perfectly 
agreed. 

The  rivets  were  all  driven  by  pressure.  They  were  of  steel 
in  all  the  steel  parts,  but  of  a  lower  grade  than  the  pieces  in 
which  they  were  driven. 

For  further  information  upon  riveting  and  tests  see  appendix. 

ERECTION. 

In  March,  of  the  present  year,  I  returned  to  Suspension 
Bridge  to  make  arrangements  for  erection. 

An  examination  was  made  of  the  condition  of  the  lower 
floor  beams.  From  this  examination  it  was  evident  that  the 
beams  were  not  in  a  suitable  condition  to  sustain  the  extra 
weight  that  would  come  upon  them  while  the  new  work  was 
being  erected,  from  the  fact,  that  in  addition  to  the  natural  de- 
terioration they  would  require  deep  notches  cut  into  them,  thus 
weakening  them  still  further. 

Consequently  I  decided  to  put  the  new  iron  beams  in,  nearly 
throughout,  before  commencing  the  work  of  erection  proper. 

A  commencement  was  made  upon  this  April  13th,  1880,  but 
it  did  not  go  forward  rapidly  until  the  21st  of  that  month. 
The  work  began  at  the  middle  and  proceeded  toward  each  end. 
As  it  went  forward  the  floor  was  taken  up  for  a  width  of  about 
3  feet  on  each  side  and  a  temporary  wooden  railing  was  put  up 
on  each  side  of  the  carriage  way,  leaving,  for  that  purpose,  a 
space  of  9  feet  in  width. 

As  soon  as  an  old  beam  was  taken  out  an  iron  beam  was  put 
in  its  place,  the  suspenders  attached  to  its  ends,  and  the  old 
chords  and  posts  firmly  secured  to  it. 

This  part  ot  the  work  was  done  by  May  13th.  On  the  31st 
of  May,  most  of  the  material  having  arrived,  we  started  on  the 
work  of  erection.  At  that  time  we  had  stripped  the  old  bridge 
of  all  superfluous  material,  as  cornices,  the  rails  forming  the 
broad  gauge  track,  &;c.,  in  all  decreasing  the  weight  about 
80  tons. 

METHOD  PURSUED  IN  ERECTING  THE  NEW  WORK. 

Plate  IV  is  given  to  show  the  respective  positions  of  the  old 
and  new  work. 


I,. 


1 1 

ill 

i  ■ ' 


26 

The  new  superstructure  is  made  as  wide  as  would  admit  of 
its  being  placed  between  the  rods  of  the  two  old  trusses.  The 
bottoms  of  the  iron  lower  floor  beams  were  placed  at  the  same 
level  as  those  of  the  old  beams.  The  tops  of  the  new  upper 
beams  were  about  an  in  inch  below  the  tops  of  the  old  ones  at 
the  ends. 

The  steel  upper  chords  are  3  inches  narrower  than  the  lower 
ones,  in  order  that,  by  cutting  away  3  inches  in  width  from  the 
inner  edges  of  the  wooden  chords  and  notching  the  tops  of  the 
wooden  floor  beams,  the  steel  chord  could  be  placed  in  poHtion. 

The  outer  channel  of  the  lower  chord  came  in  the  position 
of  the  foot  of  the  inner  hall  ot  the  old  post. 

The  erection  proceeded  as  follows : 

1st.  Blocks  of  pine  4  in.  x  6  in.  and  of  various  lengths  were 
prepared  and  tacked,  one  to  the  foot  of  each  post,  (the  lower 
ends  of  the  old  posts  consisted  of  blocks  of  red  cedar.) 

2d.  Beginning  at  the  middle  of  the  bridge  five  lengths  of 
steel  lower  chord  were  placed  in  position,  on  each  side  of  the 
lower  floor.  The  red  cedar  blocks  being  removed  to  make  room 
for  them,  and  as  soon  as  a  length  of  chord  was  placed,  the  new 
4  in.  X  6  in.  blocks  were  inserted  between  the  foot  of  the  inner 
half  of  the  post  and  top  of  the  steel  chord. 

As  the  chords  were  placed  their  splices  were  riveted  up. 
The  rivets  for  this  purpose  are  of  steel  from  f  in.  to  ^  in.  diam- 
eter. They  were  driven  while  hot,  with  8  to  10  lbs.  sledges, 
which  had  the  effect  of  upsetting  the  rivet  and  making  it  fill 
the  hole  nearly  as  well  as  by  pressure. 

3d.  Beginning  at  the  middle  again,  one  part  of  each  upper 
floor  beam  was  cut  off  and  the  middle  portion  taken  out  to 
make  room  for  the  iron  beams.  These  were  inserted  by  passing 
them  through  between  the  old  track  stringer,  turning  them  up 
on  edge  and  placing  them.  As  soon  as  the  iron  beam  was  in 
place  a  pair  of  steel  posts  were  set  up,  the  lower  chord  pins 
passed  through  the  chord,  the  foot  of  the  posts,  and  the  eyes  of 
the  truss  rods  stubs.  The  heads  of  the  two  posts  were  then 
placed  under  the  ends  ol  the  upper  beam  and  temporarily 
bolted  to  its  lower  flanges.  The  beam  was  then  wedged  fiimly 
between  the  parts  of  the  old  track  stringer  with  wooden 
wedges. 


1 


27 


d  admit  of 
isses.  The 
it  the  same 
new  upper 
)ld  ones  at 

the  lower 
li  from  the 
ops  of  the 
n  pof'ition. 
5  position 


gths  were 
the  lower 

3ngths  of 
ie  of  the 
ike  room 
the  new 
;he  inner 


Jted  up. 
n.  diam- 
sledges, 
g  it  fill 

3  upper 
1  out  to 
passing 
lem  up 
was  in 
rd  pins 
eyes  of 
e  then 
orarijj 
fiimij 
'ooden 


4th.  As  soon  as  twelve  of  the  new  bents  were  placed,  three 
lengths  of  upper  steel  chord  were  placed  in  position,  on  each 
side  and  bolted  to  the  top  flanges  o(  the  iron  beams.  Their 
splices  were  then  riveted. 

5th.  The  new  truss  rods  were  then  inserted.  They  are  in 
pairs,  made  of  1^  in.  square  iron.  Each  rod  is  in  two  pieces. 
Each  piece  has  an  eye  at  one  end  and  a  thread  cut  on  the  other. 
The  piece  in  the  lower  chord  is  short  and  has  a  left  hand  thread 
cut  on  it.  The  two  parts  are  connected  and  adjusted  by  a 
sleeve  nut.  Each  rod  extends  from  the  foot  of  one  post  to  the 
top  of  the  third  post  from  it,  and  they  incline  each  way. 

In  erecting,  but  one  rod  was  put  in  each  place  at  first  in 
order  to  save  weight. 

In  the  above  order  the  work  proceeded  each  way  from  the  mid- 
dle of  the  bridge  toward  each  end, 

6th.  When  150  feet  of  the  new  work  was  in  place,  the  new 
chords  were  securely  clamped  to  the  old  by  means  of  oak  and 
pine  timber. 

In  the  case  of  the  upper  chord  the  timber  was  notched  to  the 
pin  ends,  rivet  heads,  &c.,  at  the  side  of  the  steel  chord  and 
resting  on  the  top  of  the  wooden  chord.  The  upper  side  of  the 
wooden  chord  and  the  under  side  of  the  timber  were  notched 
at  intervals  for  the  reception  of  oak  keys.  The  timber  was 
then  clamped  strongly  to  both  old  and  new  chords,  and  the 
keys  inserted  in  the  notches. 

The  old  and  new  lower  chords  were  clamped  by  fitting 
pieces  of  4  in.  x  16  in.  pine  to  the  lattice  straps  and  rivet  heads 
on  the  under  side  of  the  steel  chord.  It  was  keyed  to  the  top 
of  the  auxiliary  chord.     The  whole  was  then  bolted  together. 

7th.  As  soon  as  the  clamps  were  secured,  the  work  of  renew- 
ing the  old  material  was  commenced  at  the  middle  of  the 
bridge,  and  followed  that  of  erecting  the  new,  generally,  with, 
an  interval  of  about  75  feet  each  way. 

The  portion  of  the  new  work  thus  put  in  place  weighed 
about  1,100  lbs.  per  running  foot  of  bridge.  Hence  there  were 
seldom  over  90  tons  of  new  material  overlapping  the  old,  but 
at  the  start,  being  in  the  middle,  this  was  equivalent  to  about 
150  tons  distributed,  or  deducting  the  80  tons,  saved  by  strip- 


28 


'I 


m 


f 


M'' 


ping  the  bridge,  we  have  lef «  70  tons  as  the  probable  extra  dead 
load  upon  it,  but  as  the  trains  had  at  the  outset  been  limited 
to  190  tons,  it  is  not  probable  that  the  total  weight  of  live  and 
dead  load  ever  exceeded  that  of  ordinary  usage. 

While  the  above  rhanges  were  being  made,  the  work  of  re- 
placing the  lower  floor  was  going  forward  each  way  from  the 
middle.  As  the  planking  of  the  old  floor  was  laid  longitudi- 
nally, while  that  of  new  is  laid  transversely,  there  was  neces- 
sarily a  gap  between  them,  which  was  bridged  over  by  a  raised 
platform,  under  v/hich  the  change  was  made,  and  which  was 
moved  along  as  the  work  progressed. 

When  the  work  of  making  the  above  changes  had  reached 
the  towers  that  of  completing  the  riveting  was  carried  through. 
It  was  all  completed,  except  changing  the  track,  by  the  25th 
of  August.  Up  to  that  time  the  traffic  had  not  been  inter- 
rupted. 

10th.  After  the  work  of  replacing  the  trusses  and  floors  was 
completed,  that  of  renewing  the  track  began  at  the  middle  and 
proceeded  each  way  at  the  rate  of  30  feet  per  day,  or  of  60  feet 
total.  This  could  have  been  done  without  interrupting  traffic, 
but  as  the  Great  Western  Hallway  Company  was  to  do  the 
work  of  removing  the  old  material  of  the  track  and  put  on  the 
new  timber,  they  preferred  to  take  an  hour  each  day,  when 
there  was  no  passenger  train  and  scarcely  any  freight  to  cross, 
and  make  the  change  of  60  feet  at  one  time.  This  gave  the 
remainder  of  the  day  to  preparing  more  old  material  for  re- 
moval, and  for  completing  the  riveting  of  the  new. 

The  whole  change  was  completed  September  I7ih.  Since 
the  completion  of  the  changes  above  described  the  time  has 
been  occupied  in  making  side  walks,  hand  rails,  putting  on  the 
new  roof,  making  new  fastenings  for  the  overfloor  stays  at  the 
saddle,  on  the  towers,  and  in  painting. 

The  brick  houses  have  also  been  built  to  cover  the  strands 
at  the  ends  of  the  cables. 


ADJUSTMENTS. 

The  work  of  adjusting  the  new  structure  has  been  carried 
forward  as  rapidly  as  circumstances  would  permit. 


■■an 


29 


The  operation  was  as  follows : 

Ist  To  Adjust  the  Camber. — It  was  desirable  to  make  it  as 
nearly  an  arc  of  a  circle  as  possible.  Consequently  the  truss 
rods  were  slackened  in  order  to  allow  the  cables  to  assume  their 
natural  curves.  Levels  at  each  100  feet,  in  the  length  of  the 
bridge,  jvere  taken  to  ascertain  its  profile  while  hanging 
naturally,  then  the  true  arc,  with  a  proper  versedsine  for  mean 
temperature  was  calculated,  after  which  the  difference  between 
the  true  arc  and  the  actual  camber  was  found  for  each  of  the 
points.  The  suspenders  were  then  screwed  up  or  unscrewed 
according  as  the  structure  required  raising  or  lowering  till  the 
proper  camber  was  given.  As  this  raising  or  lowering  pro- 
gressed it  was  necessary  to  keep  the  rods  slackened. 

2d.  Stress  on  Suspenders. — This  adjustment  was  made 
by  means  of  a  hydraulic  weighing  machine.  A  portable 
wooden  frame  was  made  to  rest  against  the  under  sides  of  the 
beams.  One  end  of  the  machine  was  secured  to  a  screw  passing 
through  a  cross  beam  of  this  frame  while  the  other  end  of  the 
machine  w..s  attached  to  the  screw  end  of  the  suspender.  The 
nuts  on  the  screw  ends  were  then  slackened  off".  Then  by 
working  the  screw  at  the  other  end  of  the  machine  the  right 
strers  was  given  to  the  suspender  as  indicated  by  the  index. 

The  first  time  of  going  over  them  the  machine  was  attached 
to  one  of  the  suspenders  and  the  proper  stress  given  to  it. 
Then,  leaving  the  machine  in  that  position,  the  five  or  six  sus- 
suspenders  on  either  side  of  it  were  adjusted  by  springing  them 
laterally  with  the  hand,  using  the  suspender  with  the  machine 
on  it,  as  the  standard.  After  going  over  them  in  this  way  from 
one  end  to  the  other  the  machine  was  tried  upon  an  occasional 
suspender  to  verify  the  stress.  This  required  to  be  gone  over 
three  times  to  bring  them  to  proper  adjustment. 

3d.  Truss  Rod  Adjustment. — The  truss  rods  required  to  be 
adjusted  at  about  mean  temperature,  at  which  time  there  should 
be  no  stress  upon  any  of  them  when  the  bridge  is  unloaded. 

Consequently  at  about  mean  temperature  each  of  a  pair  of 
rods  was  first  screwed  up  to  an  equal  bearing  and  then  the 
sleeve  nuts  were  turned  backward  just  half  of  a  revolution. 
This  gives  the  trusses  a  little  more  flexibility,  decreasing  the 


1$ 


SO 
temperature  stresses  and  Af  fi 
»°«than  the  proper  amoU    or^'r":'  '^"^^  -'allow  of 

were  adjusted  by  ru„„i„g  ,  ^f^/"";;  f.^ndred  feet  ou-,  they 
«.-  -e.i„,  e.h  or  thf  .a/s'^tolfpr^X.^ ""  ""^ 
mSENT  ARBANGEMENT  OE  THE  BRIDGE 

-HorrHr:^^::^^-,:-;^;  e.eept.-o„  on.e 

■Plates  II  and  Tfl  »h        /  described. 

But  the  action  or  so  „e  If  1?™"^^"'^"'  "^  ">«  t^ss  system 

«on  bndge  of  this  sort,  i„  order!  ,    T  ?'"''' '"  "^  ™^Pen- 

(or  those  from  the  tops  of  th^T  ''^  ""^  """'^o^'  stays 

floors)  effective,  a  con'ltt '  rruf  .'^''^«'»'  ?"■■"«  of  the 

point  of  whose  length  shall  bTsl",  '' r^"^-  '^e  ".iddle 

The  trusses  in  this  ease  are  cont Ln!!' V  "'""'■'^  "'"  Po^^iW"- 

order  to  keep  the  middle  ftom  mo  ""  *"<'  '"  «"d.     I„ 

automatic  device  shown  at  "he  ZdJ  .'"?'''  "'"'«'  '"^  'he 

n  and  m,  „,,  designed.     Its  ^L    ^  '""'''  '=''"''•  ^'^'es 

In  the  prolongation  of  the    „e  of  t."  f"^"^^  ''  ''""""s : 
ment  casting  A  (Plate  Iliriirmlv    '       T'  "^""^  '»  »"  "but- 
'he  arch.     This  casting  received  the     T'^'"  '^'  ™^«°'»'y  of 
There  is  one  of  these  fast  n's    ,  tch'e  ;';"'  "'  ">«  «''"'». 
A  bent  lever  B  ha^  .-.s  fulcrum  fit     ^   '"      '"*«■•  "hord. 
P)  of  the  short  arm  ...  the  leve^  ;!  t""''''''  '^  ^-    A'  'he  end 
diameter  round  rod  R      Th i,     V       "^^"^  °"^  ^"d  of  a  f  in 
chord  to  the  oppositf  sid?:f  Ihe  ^'^"'^^"-^o-gh  the  lowe; 
secured  to  the  abutment  castl  h  '  7^'"'  "'  °'her  end  is 

of  .'he  long  arm  of  B  is  susp  /ded^"  ""'  "^^  ^'  "'<'  cd  (F) 
IS  mterposed  between  the  endc^'^l^t  "?"  "^"^^  «•  «hich 
men.  casting.     The  action  of  the  d,  •'  "^°''"  ""'^  "^  *he  abut- 

The  change  i„  length  of    he  X    ^'t "' ^"""^^  ^ 
'emperature,  is  about  8^  inche       If  ^K  '  ^'.''"'"  ^^^^'"es  of 


81 


extremes.  The  rod  R,  whicli  lies  loosely  in  the  chord  but 
otherwise  is  independent  of  it,  is  a  little  longer  than  the  chord 
and  will  change  in  length,  between  extremes,  8^  inches,  or 
double  the  movement  of  either  end  of  the  chord.  Hence  the 
other  end  of  the  rod  being  fast,  the  end  D  will  move  8^  inches 
carrying  the  end  of  the  lever  with  it  at  the  same  time  that  the 
end  of  the  chord  moves  4J  inches.  Arm  E  F  of  the  lever  is 
three  times  the  length  of  D  E,  hence  F  will  move  25^  inches, 
or  six  times  as  far  as  the  end  of  the  chord  moves.  Consequently 
the  wedge  C  is  made  with  an  inclination  1  to  6  of  its  length. 
There  is  one  ot  these  wedges  at  each  end  of  each  lower  chord. 
When  the  chord  contracts  the  rod  contracts  in  the  same  pro- 
portion and  at  the  same  time,  thus  bringing  a  thicker  part  of 
the  wedge  between  the  chord  and  abutment. 

There  is  half  an  inch  of  space  at  each  end  for  the  chord  to 
go  and  come  in  before  bearing  upon  the  wedge,  an  amount 
which  is  very  nearly  constant  for  all  temperatures. 

The  long  rods  lymg  inside  of  the  chcrd  they  both  keep  at 
nearly  the  same  temperature  with  each  other. 

The  wedge  has  two  g-  rfaces  of  friction,  and  hence  its  incli- 
nation of  1  to  6  is  far  within  the  angle  of  friction  of  cast  iron. 
Hence  no  matter  what  the  pressure  of  the  chord,  it  brings  no 
stress  upon  rod  R  except  what  is  required  to  sustain  the  weight 
of  the  wedge. 

Should  the  wedge  ever  get  caught  by  the  chord  remaining 
against  it,  there  being  scarcely  two  hours,  day  or  night,  in 
which  a  train  does  not  pass,  as  soon  as  a  train  rests  on  the  other 
end  of  the  bridge  the  wedge  will  be  released. 

Fig.  1,  Plate  VI  is  to  show  the  action  above  described. 

2d.  Action  of  the  Overfloob  Stays  —Fig.  1,  Plate  VI  is 
to  assist  in  explaining  this. 

In  case  of  a  wooden  truss,  the  points  of  attachment  of  the 
stays  to  the  floor  move  in  vertical  lines  as  the  temperature 
changes.  Their  change  in  length  is  not  sufficient  to  compensate 
for  the  amount  that  the  cables  move  the  floor  vertically. 
Hence,  if  they  are  adjusted  properly  for  cold  weather,  they 
will  become  so  tight  in  summer  as  to  break  and  vice  versa.  In 
the  case  of  an  iron  truss  with  a  slip  joint  anywhere  beyond  the 


82 


ill! 


ifi: 


attachment  of  the  stays  and  with  the  end  of  the  truss  fixed  at 
the  tower,  the  point  of  attachment  will  move  in  a  line  c  d, 
in  which  case  its  action  is  worse  than  in  that  of  a  wooden 
truss. 

But  in  the  case  of  a  continuous  truss  with  the  middle  kept 
stationary,  the  point  of  attachment  moves  in  the  line  a  b.  In 
this  way  the  stay  is  made  to  compensate  very  nearly  for  all 
changes  of  temperature. 

3d.  The  ends  of  the  trusses  are  anchored  to  prevent  vertical 
and  lateral  movement  only. 

At  the  New  York  end  this  is  effected  by  a  hinged  strut 

At  the  Canada  end,  where  the  surface  of  the  rock  is  nearly 
at  the  level  of  the  lower  floor,  a  casting,  anchored  to  the  rock, 
is  provided  with  slots,  in  which  blocks  on  the  ends  of  the  end 
pins  of  the  lower  chord  are  free  to  move  in  the  direction  of  the 
length  of  the  bridge  only. 

4th.  Suspenders. — On  account  of  the  ends  of  the  trusses 
being  anchored  to  the  rock  the  suspenders  near  the  ends  require 
to  be  left  slack.  It  would  be  as  well  if  they  were  left  off,  but 
as  they  do  no  harm  they  were  kept  on  more  for  appearance 
sake  than  otherwise. 

5th.  Upper  Floor. — The  deep  transverse  beams  of  the 
upper  floor,  together  with  the  deep  longitudinal  track  stringers, 
distributing  the  load  over  several  beams,  and  the  upper  cable 
suspenders  attaching  to  the  beams,  as  shown  in  the  transverse 
view,  Plate  II,  form  a  very  stiff  floor.  This  makes  the  office 
of  the  knee  braces  that  of  steadying  the  bents  merely. 

6th.  Lower  Floor. — The  planking  of  the  lower  floor  is  laid 
crosswise  ot  the  bridge  and  in  one  thickness,  to  enable  water 
to  drain  off  more  readily  and  the  floor  to  dry  out  quickly. 

The  narrow  foot- walks  at  each  side  serve  the  double  purpose 
of  a  clean  walk  for  pedestrians  and  to  prevent  the  snow  being 
blown  from  the  carriage-way  in  winter,  while,  at  the  same  time, 
they  confine  the  portion  loaded  with  snow  to  the  necessary 
width  for  carriages  to  pass  each  other. 

7th  Lateral  Bracing. — As  neither  the  upper  or  lower 
floor  has  any  longitudinal  planking  to  afford  lateral  stiffness, 
diagonal  rods  of  steel  were  introduced  to  supply  the  deficiency. 


MM 


33 

The  fiftysix  wire  rope  river-stays  are  retained  to  resist  the 
action  of  high  winds  and  consequently  the  diiigonal  rods  are 
merely  for  the  purpose  of  keeping  the  intermediate  points  of 
tiie  cliords  in  line. 


STRENGTH  OF  THE  BRIDGE. 

The  anchorage,  cables  and  towers  are  ])rimarily  the  support- 
ing members  of  the  bridge  as  before.  Hence  the  strength  of 
these  members  is  to  be  considered  first,  in  the  order  observed 
above. 

1st.  The  Strength  of  the  Anchorage. — This  has  already 
been  discussed  under  the  head  of  Reinforcement  of  Anchorage. 

2d.  The  Cables. — The  number  of  wires  in  each  of  the  four 
cables  is  3,640.  The  original,  average,  ultimate  strength  of 
each  wire  was  1,648  lbs.  This  gave,  as  the  strength  of  one 
cable,  3,640  x  1,648=5,998.720  lbs.=2,989  tons,  or  for  the 
four  cables=2,999  x  4=11,996  tons  in  the  direction  of  their 
length.  There  is  no  indication  of  any  deterioiation  in  their 
strength,  but  su])pose  the  strength  of  the  four  cables  to  be  11,- 
000  tons  in  the  direction  of  their  length,  or  1,511  lbs.  per  wire. 

The  present  total  suspended  weight  of  bridge,  between  the 
towers  and  including  cables  and  stays,  is  1,050  tons.  Taking 
the  maximum  live  loud  upon  the  bridge  at  one  time  as  350  tons 
it  makes  the  total  live  and  dead  ]oad==l,4'^0  tons.  The  maxi- 
mum stress  upon  the  cables  is  at  the  top  of  the  tower.  Their 
stress  at  this  point,  in  the  direction  of  their  length,  is  to  the 
total  vertical  load  as  1.78  is  to  1.  Hence  we  have  -4:^''=6,180 
tons.     The  factor  of  safety  is  then  ^fSg==4.41. 

This  factor  of  safety,  in  a  tension  member  as  long  as  one  of 
these  cables,  and  where  the  load,  from  the  time  it  starts  upon 
the  bridge  till  it  produces  its  maximum  ell'ect,  is  rarely  less 
than  one  minute,  is  ample. 

3d.  The  Towers. — The  maximum  load  imposed  upon  the 
top  of  ono  tower  by  the  cables  is  700  tons,  and  acting  in  a 
nearly  vertical  direction.  The  least  section  of  the  tower  is  just 
below  the  top  and  is  64  square  feet.  Hence  the  pressure  per 
square  foot,  from  the  cable,  is  Y/==10.94  tons. 


H 

Trantwine  gives,  as  the  crushing  load  for  limestone,  250  to 
1,000  tons  per  square  foot  Hence  if  yi%  take  250  tons  as  the 
crushing  load  iirl4=23,  nearly,  is  the  factor  of  safety.  Or,  if 
a  factor  of  safety  of  10  should  be  accepted,  the  number  of 
square  feet  necessary  at  the  top  of  the  tower  would-»^^— =28 
square  feet,  or  a  square  whose  side  is  5.29  ft  There  is  no 
other  place  at  which  the  pressure  per  square  foot  is  so  great  as 
at  the  point  considered.  Hence  we  could  remove  a  thickness 
of  1  foot  4  inches  on  all  four  sides  of  the  tower  and  still  have 
it  safe. 

The  stone,  of  which  the  towers  are  made,  is  limestone  that 
was  quarried  near  the  bridge.  It  jis  very  strong  when  used 
where  it  is  not  exposed  to  moisture  and  frost,  as  for  the  inside 
of  a  wall  But  where  exposed  as  in  the  faces  of  the  towers, 
its  surface  disintegrates  or  "flakes  off,"  and  if  neglected, 
would  in  time  work  in  to  a  depth  that  would  endanger  the 
tower. 

Painting  has  been  resorted  to  as  a  protection  but  it  soon 
dries  and  cracks.  In  any  case  it  should  not  be  put  on  unless 
the  tower  is  dry  as  after  several  weeks  of  dry  warm  weather. 

It  might  be  well  to  try  a  coating  of  asphalte  mixed  with 
some  material  to  keep  it  from  cracking. 

But,  in  any  event,  the  towers  should  be  attended  to  and, 
where  necessary,  new  stones  should  be  set  in  the  faces. 


STRENGTH  OF  OTHER  PARTS. 

SusPBNDERS. — The  suspenders  have  not  been  renewed. 
There  are  628  of  them  to  sustain  a  maximum  load  of  1,025 
tons,  or  each  one  sustains  1.63  tons.  In  no  case  does  the  load 
exceed  two  tons.  They  are  of  4^  in.  circumference  wire  rope 
possessing  when  new  an  ultimate  strength  of  30  tons,  giving  a 
factor  of  safety  of  at  least  15.  I  have  examined  pieces  of  wire 
from  several  of  those  that  we  have  cut  and  tested  them  for 
bending.     There  is  no  doubt  of  their  strength  being  ample. 

The  upper  cable  suspenders  are  attached  to  the  upper 
floor  beams  by  means  of  U  shaped  stirrups  made  out  of  1^^  in. 
round  iron. 


86 

The  lower  suspenders  attach  directly  to  the  projecting  ends 
of  the  lower  floor  beams  and  close  to  the  lower  chord. 

Stay  Fastenings. — The  stays  are  of  wire  rope,  same  size  as 
the  suspenders.  The  fastenings  of  the  stays  at  the  towers  have 
been  renewed  in  a  manner  to  render  the  stays  safe  from  wear. 

The  lower  ends  of  the  upper  floor  stays  have  permanent  iron 
fastenings  riveted  to  the  iron  beams  and  tied  to  the  chords  and 
track  stringers  by  means  of  iron  bars.  The  lower  floor  and 
river  stays  are  attached  to  the  lower  chord  pins. 

In  short  it  has  been  the  intention  to  have  all  fastenings  per- 
manent, in  order  that  adjustments  once  made  will  not  be  dis- 
turbed by  any  renewals  of  wood-work  that  may  be  necessary. 

STRENGTH  OF  THE  TRUSS  SYSTEM. 

The  trusses  have  been  designed  for  a  maximum  load  of  .8  of 
a  ton  per  foot  run,  and  a  length  of  load  of  534  feet,  using  the 
formulae  given  by  Rankine  with  a  factor  of  safety  of  5. 

For  calculations  on  truss  stresses,  see  appendix. 


RESISTANCE  TO  HIGH  WIND. 

For  this  purpose  we  have  the  inclination  of  the  planes  of  the 
cables  and  the  same  number  of  wind  stays  as  in  the  case  of  the 
old  bridge,  while  there  is  less  than  six-tenths  as  great  wind- 
surface.  In  a  very  high  wind,  blowing  steadily,  the  bridge  at 
the  middle  swings  to  the  leeward  5  to  6  inches  and  remains 
there  while  the  wind  continues,  but  the  motion  is  not  felt  when 
one  is  on  the  bridge.  When  in  that  position  there  is  more  of  the 
weight  of  the  structure  thrown  upon  the  upper  windward  cable 
and  the  lower  leeward  cable,  while  the  other  two  are  relieved 
of  a  like  amount.  I  estimate  the  resistance  produced  by  the 
inclination  of  the  cable  planes  alone  in  that  condition  at  30 
tons.  There  are,  at  the  same  time,  the  28  river  stays  on  each 
side.  Those  on  the  leeward  side  are  relieved  while  the  stress 
on  those  of  the  windward  side  is  greatly  increased.  As  this 
resistance  is  partly  downward  and  partly  toward  the  wind  they 
not  only  increase  the  resistance  offered  by  the  cables  but  will 
safely  afford  a  direct  united  resistance  of  160  tons.     The  8,000 


86 


square  foot  of  wind  surface,  taking  the  pressure  of  the  wind  at 
50  lbs.  j)cr  square  foot,  gives  400,000  11)8  —  200  tons  pressure. 
Wliere  tlie  wind  blows  in  gusts  it  does  not  appear  to  ull'ect  the 
bridge  perceptibly. 

None  of  the  unusually  high  winds  of  this  fall,  though 
blowing  directly  across  the  bridge,  allected  it  siifliciently  to  be 
felt  by  a  person  standing  on  it. 

The  strength  of  the  trusses,  together  with  the  overflow  and 
river  stays,  will  eflectually  prevent  any  vertical  undulation 
from  the  eil'ect  of  wind. 


WEIGHT  OFTIIK  NEW  STRUCTURE  COMPARED  TO 

THAT  OF  THE  OLD. 

The  weight  of  the  wooden  structure,  at  its  con]})letion,  wjis 
estimated  by  Mr.  John  A.  Roebling  at  1,000  tons.  But  at  the 
date  of  the  inspection,  there  having  been  a  large  nmount  of 
titnber  added  to  it,  it  was  estimated  to  wei^h  1,180  tons. 

When  the  work  of  replacing  the  lower  iioor  btams  was  in 
progress  I  liad  one  of  them  weighed  and  found  that  owing  to 
the  amount  of  water  that  it  held  it  wa.^  veiy  nmcli  lieavier  than  it 
had  been  estimated.  I  also  weighed  other  pieces  of  the  bridge 
and  from  these  made  a  new  estimate  with  the  following 
result : 
Total  suspended  weight  between  the  j  Old  bridge,  1,228  tons. 

towers,        -  -  •         ]  New     "         1,050      " 

Difference  in  favor  of  new  bridge,         -  •  178      " 

It  is  possible  that  the  estimate  of  1.228  tons  is  somewhat  in 
excess.  But  as  the  new  bridge  is  now  higher  in  the  middle 
than  the  old  one  for  the  same  temperature,  notwithstanding 
that  the  middle  suspenders  have  been  lengthened  over  3  inches 
since  its  completion,  that  would  indicate  a  decrease  of  consider- 
ably over  100  tons. 

SUGGESTIONS  REGARDING  THE  CARE  OF  THE 

BRIDGE. 

1st.  As  soon  as  dry  weather  comes  next  spring  it  would  be 
well  to  remove  the  hatchway  covers  from  anchorage  houses, 


1( 


87 

and,  if  tliere  hIiouM  he  any  dampnoss,  let  tlicm  dry  tlioronghly 
uikI  tluMi  juiint  all  t;xi)f)S(Ml  inm  work  and  win-s.  TluMe  is  not 
much  prohability  of  danij)no.sM  as  there  is  ample  ventilation  at 
top  ami  hottom,  but  the  covers  should  he  removed  once  a  year 
and  left  off  during  one  warm,  dry  day,  and  any  part  painted 
which  appears  to  need  it. 

2d.  The  ca|)a  on  top  of  the  towers  had  better  be  removed  at 
the  same  time,  the  parts  painted  and  niaeliine  oil  put  in 
around  the  edges  of  the  saddles. 

An  examination  of  the  cables,  from  time  to  time,  will  enahle 
an  experienced  num  to  determine  when  tliey  i-rrpiire  paintijig. 
They  should  be  [tainted  a>  olten  as  the  paint  gets  so  hard  and 
drv  Jis  to  crack. 

2(1.  The  new  work  should  be  ])aintcd  whenever  it  requires 
it  Those  portions  near  the  intersections  of  chords,  beams, 
posts,  &c.,  will  rcfpiire  painting  oftener  than  other  parts. 

3d.  Spkkd  of  Trains. — The  durability  of  the  bridge  and 
(in  case  of  derailment)  the  safety  of  the  trains  render  it  ad- 
visable that  some  more  ellicient  means  should  be  adopted  for 
enforcing  the  article  of  agreement,  limiting  the  s])eed  of  trains 
on  tlie  bridge  to  live  miles  per  hour. 


SUPERINTENDENCE. 

A  competent  superintendent  will,  of  course,  continue  to  be 
necessary. 

I  trust  that  it  will  not  be  considered  out  of  place  ior  me  to 
say  here,  that  judging  from  my  acquain  ance  with  Mr.  W.  G. 
Swan,  it  is  my  opinion  that  no  better  man  than  he  can  ))e  found 
to  fill  the  position.  He  has  at  all  times  shown  himself  to  be 
conscientious  in  the  discharge  of  h\?.  duties,  is  acquainted  with 
all  the  details  of  the  bridge,  and  will  therefore  be  competent 
to  judge,  by  inspection,  of  what  is  required  from  time  to  time 
for  its  preservation. 

In  concluding  this  report  I  wish  to  express  my  sense  of 
obligation  to  the  Bridge  Companies'  Superintendent,  Mr.  W.  G. 
Swan,  for  the  willing  assistance  he  has  always  rendered  in 
promptly  supplying  me  with  necessary  tools  and  materials,  as 
well  as  for  his  friendly  interest  in  the  success  of  my  work. 


88 


Also  to  the  Pittsburgh  Bridge  Co.  who,  in  supplying  the 
iron  and  steel  materials,  called  for  by  my  plans,  never  spared 
any  pains  necessary  to  secure  materials  and  workmanship  of 
an  entirely  satisfactory  nature. 

Nor  must  I  neglect  to  award  great  credit  to  my  foreman,  Mr. 
William  Gardner,  and  to  the  workmen,  who,  by  careful  atten- 
tion to  orders,  did  so  much  toward  enabling  me  to  complete, 
and  without  an  accident,  a  work  that  otherwise  would  have 
been  dangerous. 

In  resigning  my  position  as  engineer  of  the  work,  I  take 
pleasure  in  acknowledging  to  the  Presidents  and  gentlemen  of 
both  Boards  of  Directors  my  indebtedness  for  their  kindness 
toward  me  and  for  the  unvarying  confidence  they  have  mani- 
fested in  my  professional  judgment. 

L.  L.  BUCK. 


P 
$ 


APPENDIX. 


ive  mani- 


CALCULATION  OF  STRAINS  UPON  THE  TRUSSES. 

The  formulsB  given  in  Rankine's  Applied  Mechanics,  for 
"  Stiflfened  Suspension  Bridges  "  have  been  principally  the  ones 
used  in  the  following  calculations,  but  with  some  modifications 
deduced  from  observation  of  the  action  of  the  old  bridge  under 
partial  loads. 

The  formulae  in  question,  except  in  one  instance,  treat  the 
stiffened  suspension  bridge  as  an  inflexible  structure,  which,  of 
course,  cannot  be  the  case  in  pra-tice,  though,  by  giving  to  the 
trusses  greater  depth  in  proportion  to  their  length,  we  could 
approximate  to  the  supposed  condition.  But  it  would  be  an 
unnecessary  condition  in  any  case,  and  as  before  explained,  is 
not  admissable  in  the  one  here  considered. 

The  old  truss  system  of  the  bridge  was  very  flexible,  deflec- 
ting under  partial  live  loads,  in  some  cases  as  much  as  2  feet 
in  a  length  of  500  feet.  Yet  the  trains  passed  over  it  easily, 
and  after  twenty-five  years  of  constant  use,  the  cables  give  no 
indications  of  ill  eflfects  from  the  undulations. 

In  designing  the  new  trusses  I  considered  a  maximum  deflec- 
tion of  15  inches  in  a  length  of  500  feet  as  not  at  all  excessive. 
Fig.  2,  Plate  V,  is  given  to  illustrate  the  advantage  that  is 
gained  by  giving  to  the  trusses  considerable  flexibility,  aside 
from  the  relief  it  affords  to  the  cables  in  bending  the  trusses  at 
low  temperature. 

By  allowing  a  deflection  of  15  inches  in  a  length  of  500  feet 
it  was  estimated  that  the  intensity  of  the  live  load,  per  running 
foot  of  bridge,  and  to  be  used  in  the  formulse,  was  reduced  by 
.2  ton.  In  other  words,  if  the  trusses  and  cables  were  perfectly 
flexible  it,  would  require  two-tenths  of  a  ton  per  foot  run  to 


11 


•  1 ' 


produce  the  given  deflection.  The  total  intensity  was  taken  at 
eight-tenths  ot  a  ton.  Deducting  the  two-tenths  of  a  ton  we 
have  six-tenths  of  a  ton  to  use  in  the  formuJie. 

The  formuke  are  us  follows : 

For  bending  moment  of  trusses  when  the  load  begins  at  one 
end  ot  the  bridge  and  covers  a  given  portion  of  it,  we  have  for 
the  unloaded  segment — 

M=^^'li:-,^>JH:=^^  (1) 


16  c 


The  moment  for  the  loaded  segment  is — 


M= 


_W    (C  +  X)  8    (C  —  X) 


16  c 


Max.  M=Max.  M='^"' 

C  ft  ^  f 


For  shearing  with  the  load  as  above  we  have — 

F=^ 


_W   (C8  —  X8) 

To 


Max.  F= 


w  c 


(2) 
(3) 

(4) 
(5) 


For  deflection  of  the  loaded  segment  when  the  load  covers 
two-thirds  of  the  spun  beginning  at  one  end — 


5 

27 


V- 


1C8 

e7 


(6) 


The  formula  for  a  distributed  load,  covering  the  whole  span 
and  required  to  bend  the  two  trusses  12  inches,  is  taken  from 
Moseley's  Mechanics  and  is — 


W= 


_Dy  48  EI 

5  C8 


For  chord  strain  produced  by  W,  we  have— 

S=y^=strain  per  square  inch. 

In  the  above  formulas. 
W==intensity  of  live  load  per  foot  run=.6  tons, 
c  =  half  span  of  truss=400  feet. 
X=  distance  from  middle  of  span  to  end  of  load, 
f  =  strain  per  square  inch,  on  chord  in  lbs. 
c  =  half  span  of  truss  in  inches=4,800  inches. 
E=  modulus  of  elasticity  of  steel=28,000,000. 
y  =  half  depth  of  truss  in  inches=105.5  inches. 


(7) 


(8) 


■■ns" 


D 

I 

d 
a 


111 

=  deflection  at  middle  of  truss  from  temperature=12  inches. 

=  Moment  of  Inertia  of  two  trusses=l,113,000. 

=  length  of  truss  in  feet=800. 

=  depth  of  truss  in  feet=17.58. 

=  area  of  section  of  two  chords=60  square  inches. 


LOAD  STEAINS  ON  TRUSSES. 
From  (3) 

Max.  M=^xi^U7,lll  tons. 
Hence  strain  per  square  inch  on  chord  section= 


7111 


(a) 

S=i7liR^o=8  09  tons=16,180  lbs.  (b) 

Y=:^.     1M80X  230X23.040.000      ^  . 

a  27        28,000,006x105.5    =^o.6o  inches.  (c) 

^=-^%^=5S.26  tons=106,520  lbs.  (d) 

There  may  be  two  cases  in  which  a,  h,  c  and  d  will  occur: 
1st  When  the  load,  beginning  at  one  end  of  the  span,  covers 
two-thirds  of  its  length,  in  which  case  S  is  at  the  sections  of 
the  chords  at  the  middle  of  the  loaded  segment— the  lower 
chord  being  in  tension  and  the  upper  in  compression.  At 
same  time  (c)  is  the  deflection  of  the  middle  point  of  the 
loaded  segment,  while  (rf)  is  at  the  ends  of  the  loaded  segment, 
a,  c  and  d  all  act  downward. 

2d.  When  the  load  begins  at  the  end  of  the  span  and 
covers  one  third  of  its  length,  the  eflfect  upon  the  unloaded 
segment  is  the  same  as  in  the  first  case  upon  the  loaded  segment, 
except  (a),  (c)  and  (d)  all  act  upward  and  (b)  is  tension  on  the 
upper  chord  and  compression  on  the  lower. 


Max.  F=:^°=60  tons=120,000  lbs. 


(e) 


e  occurs  when  one-half  the  span  is  loaded  beginning  at  one 
end  of  the  bridge.  It  acts  downward  at  the  extremities  of  the 
loaded  segment,  and  upward  at  the  extremities  of  the  un- 
loaded  segment 


IV 


STRAIN  Dl'E  TO  TEMPERATURE. 

At  mean  temperature  iliere  is  no  strain  upon  the  parts  of  the 
trusses  when  unloaded. 

But  in  winter  the  cables  rising  12  inches  lift  the  trusses 
the  same  amount  while  in  summer  their  own  weight  bends  them 
downward  12  inches.  In  both  cases  it  is  a  question  of  bending 
a  girder  12  inches  by  a  distributed  load  of  uniform  intensity. 
Then  by  (7) 


W= 


12  X  4R  X  28,000,000  X  1.113.000 


6  X  110,692,000,000 


=32,462  lbs. 


From  (8) 


S= 


82,462  X  800 


=3,692  lbs. 


(9) 


(h) 


8X17.58X60 

(g)  acts  upward  in  winter,  producing  a  shearing  strain  which 
is  greatest  at  the  ends  of  the  bridge  and  equals — 

w_32^_^g  231  lbs.  (t) 

(g)  acts  downward  in  summer  with  the  same  force  at  the 
ends  of  the  bridge=^^  lbs.=16,231  .bs. 

(h)  acts  on  the  chords  at  the  middle  of  their  length.  In 
winter  it  is  compression  on  the  lower  and  tension  on  the  upper. 

In  summer  it  acts  at  the  same  points  but  reverses  the  direction 
of  the  strains  on  the  chords.  The  strain  on  the  chords,  due  to 
temperature,  diminish  frem  the  middle  toward  each  end  as  the 
ordinates  of  a  parabola  whose  parameter=34,077.  Hence  from 
the  equation  of  the  parabola. 

y*=2  p  X  in  which  x=134  feet. 

y»=34,077xl34=4,656,318,  y=2,137  lbs.  (k) 

{k)  gives  the  stress,  per  square  inch,  on  the  chords  at  a  point 
267  feet  from  the  end  of  the  truss,  or  where  the  maximum 
stress  from  the  load  comes. 

Examining  the  preceding  values  we  find  as  follows : 

1st.  That  to  get  the  greatest  strain  per  square  inch  on  the 
chords,  which  will  occur  at  either  extreme  of  temperature,  we 
add  (b)  and  (k)  and  have  16,180+2,137=18,317  lbs.  (l) 

In  winter  with  the  load  one-third  as  long  as  the  bridge 
beginning  at  one  end,  I  is  at  the  middle  of  the  unloaded  seg- 


ment,  is  tension  on  the  upper  chord  and  compression  on  the 
lower. 

In  summer,  with  the  load  two-thirds  as  long  as  the  bridge,  I 
is  at  the  middle  of  the  loaded  segment,  is  tension  on  the  lower 
chord  and  compression  on  the  upper. 

2d.  The  greatest  shearing  force  occurs  at  the  ends  and  is 
found  by  adding  (e)  and  (t)=120,000+16,231=136,231  lbs.  (m). 

In  winter  this  occurs  at  one  end  of  the  bridge  while  the  load 
is  at  the  other  end  and  acts  upward. 

In  summer  it  is  at  the  end  of  the  loaded  segment  and  acts 
downward. 

This  stress  is  resisted  by  six  posts,  each  composed  of  two 
6  inch  channels,  each  having  a  section  of  2.1  square  inches,  or 
the  total  section  of  6  posts  =  25.2  square  inches.  Consequently 
the  strain  per  square  inch  =  ^§Ji  =  5,406  lbs. 

The  stress  (m)  is  also  resisted  by  12  truss  rods  whose  united 
cross  section  =  15  square  inches,  the  tangent  of  whose  incli- 
nation to  the  vertical  is  1.31.  Hence  ^^"'''y^'^^  =  11,898  lbs.  per 
square  inch. 

The  anchorage  for  holding  the  ends  of  the  span  are  secured 
by  eight  Lewis  bolts,  at  each  end  of  the  bridge.  If  inches  in 
diameter  and  sunk  into  the  rock  to  a  depth  of  5  feet. 

As  before  remarked  the  above  calculations  suppose  a  deflec- 
tion ot  15  inches  at  the  middle  of  the  loaded  segment  But 
the  formula  gives  it  as  over  28  inches  which  would  decrease 
the  intensity  still  more  and  hence  reduce  all  the  quantities 
given  above. 

The  stays  will  also  diminish  the  strains  on  the  truss  members 
especially  those  subjected  to  the  shearing  force  at  the  ends. 

NOTES  ON  THE  TEST  OF  THE  NEW  WORK. 

The  actual  deflections,  under  a  load  consisting  of  an  engine, 
tender  and  thirteen  box  cars  loaded,  having  a  total  weight  of 
357  tons,  are  given  for  eight  different  positions  of  the  load  by 
Figs.  2  to  9  inclasive  (Plate  VI).  The  total  length  of  the  train 
was  465  feet.  In  the  diagrams  the  vertical  scale  is  12.5  times 
as  great  as  the  horizontal  scale.  Fig.  2,  Plate  V,  is  constructed 
from  Fig.  5,  Plate  VI. 


i 

111 


I 


'''^     =7.66  tons=16,320  lbs. 


VI 

By  applying  the  parallelogram  of  forces  to  the  two  segments 
ot  the  cable  (Fig.  2,  Plate  V),  it  is  found  that  with  the  load  in 
the  position  shown,  covering  a  little  over  half  the  span,  the 
intensity  of  the  dead  load  of  the  unloaded  segment  balances 
not  only  the  intensity  of  the  dead  load  of  the  loaded  segment, 
but  .12  ton  of  the  intensity  of  the  live  load  beside.  The  total 
intensity  of  the  live  load=|5=.77  ton.  Consequently  {w)  in  the 
formula3=.77— 12=.65  ton.     Substituting  this  in  (2)  we  get— 

j^       .65(100  +  i5)M^0»-15)_6J33  tons. 
*•  0*00 

Stram  per  square  in,  on  chords^^^g^^gp 

F=''^°""=;.— '=64.9  tons=129,800  lbs. 

Hence,  strain  per  square  inch  on  posts=5,161  lbs. 

"       "        "        "      "  truss  rods=ll,336  lbs. 

REMARKS. 

The  train  considered  in  the  above  calculation  is  about  the 
heaviest  that  will  have  occasion  to  cross  the  bridge  and  is  about 
as  heavy  as  can  be  started  by  an  engine  on  the  up  grade  of  the 
New  York  side. 

The  overfioor  stays  will  afford  a  very  considerable  assistance 
to  the  trusses,  enough  at  least  to  compensate  for  the  increased 
stress  due  to  temperature.  An  experiment  with  a  Vernier 
scale,  reading  to  rjshxs  foot,  applied  to  the  lower  chord  at  a 
point  200  feet  from  one  end  to  determine  the  elongation  of  21 
feet  of  its  length,  under  a  load  of  one  engine  and  ten  loaded 
box  cars  weighing  about  280  tons,  resulted  in  showing  an 
elongation  corresponding  to  less  than  10,000  lbs.  per  square 
inch.     The  stays  were  not  acting  at  that  time. 

The  full  and  dotted  lines  at  ends  of  Fig.  7,  Plate  VI  coincide 
very  exactly,  apparently  indicating  that  with  the  load  in  the 
position  shown,  the  trusses  are  sufficiently  rigid  to  distribute 
the  load  over  the  cables  properly  and  consequently  to  produce 
no  more  effect  upon  them  than  if  the  load  of  same  total  weight 
was  lengthened  so  as  to  cover  the  whole  span.  Figures  5  and  9, 
Plate  VI,  indicate  a  pretty  exact  adjustment  of  stays,  sus- 
penders and  truss  rods. 


Vll 


KEMARKS  ON  TESTS  OF  STEEL. 

The  tests  of  specimens  of  steel  for  the  suspended  superstruc- 
ture were  made  on  the  testing  machine  of  Mr.  W.  L.  Gill, 
manufacturer  of  car  wheels  in  Allegheny,  Pa. 

The  strains  are  given  by  a  screw  which  enables  the  operator 
to  stop  at  any  stage  of  a  test  and  jet  be  sure  of  the  stress  re- 
maining constant.  The  strains  are  indicated  by  a  beam  scale. 
Elongations  are  measured  by  means  of  a  michrometer  with  two 
screws  reading  to  j^U^  inch.  Contact  of  screws  was  indicated 
by  a  battery  being  connected  and  striking  a  bell. 

It  was  a  very  satisfactory  machine  to  work  with. 

Enough  of  the  tests  are  given  to  show  the  action  of  the 
specimens  under  severe  treatment.     (See  table  of  tests.) 

No.  4  was  cut  from  a  plate  by  a  planer.  The  tool  raised  a 
"  lip  "  on  the  corner.  In  such  cases,  shortly  after  the  specimen 
began  to  stretch,  a  nick  would  appear  in  the  "  lip  "  and  when 
the  specimen  broke  it  would  generally  be  at  that  point.  It 
would  break  by  tearing  apart. 

Nos.  5,  6,  7  and  8  were  all  cut  from  the  same  plate  to  test  the 
eflfect  of  punching  and  reaming  and  also  of  annealing.  Regard- 
ing 5  and  6  it  appears  a  little  remarkable  that  the  punched  and 
reamed  specimen  shows  a  less  elastic  limit  but  a  larger  ultimate 
than  the  plain  specime:?..  I  account  for  the  less  elastic  limit  by 
supposing  that  the  stress  was  greater  on  one  side  of  the  hole 
than  on  the  other,  hence  causing  stretch  to  begin  on  that  side 
first.  The  cause  for  the  larger  ultimate  was  no  doubt  due  to 
the  hole  having  the  same  eflfect  that  a  semicircular  groove  does 
in  a  specimen,  viz.,  by  preventing  reduction  fracture  must  take 
place  simultaneously  over  the  whole  section  instead  of  tearing. 

The  effect  of  annealing  appeared  to  be  the  same  in  nearly  all 
cases,  viz.,  to  increase  not  only  the  stretch  and  reduction  but 
also  the  elastic  limit  and  ultimate. 

No.  13  was  cut  from  the  same  bar  as  12.  It  was  nicked  on 
one  side  with  a  sharp  chisel  and  when  under  a  strain,  consider- 
ably above  the  elastic  limit,  it  was  struck  smartly  with  a  hand 
hammer  on  the  side  opposite  the  nick,  but  showed  no  weakness. 
In  breaking,  the  break  started  at  the  nick  and  gradually  made 
its  way  through  as  in  soft  iron. 


l!W! 


;;!♦'•' 


Vlll 

Nos.  14  and  15  were  for  the  purpose  of  showing  the  effect  of 
punching  without  reaming  compared  to  that  of  punching  and 
reaming.  Calling  elastic  limit  and  ultimate  of  the  punched 
and  reamed  specimen  100,  that  of  the  punched  was  for  elastic 
limit  98,  ultimate  84. 

No.  16  was  nicked  across  one  side  and  after  determining  the 
elastic  limit  it  was  subjected  to  a  strain  of  69,370  lbs.  per 
square  inch,  and  while  the  strain  was  on  it  was  struck  on  the 
side  opposite  the  nick  sufficiently  hard  to  bend  it  J  inch  and  it 
retained  a  bend  of  ^  inch  with  the  strain  on  it. 

Nos.  17  and  17 '  were  the  same  specimen.  The  elastic  limit 
and  modulus  were  first  determined.  It  was  then  pulled  to  the 
maximum  after  which  the  strain  was  removed.  The  specimen 
measured  for  length  and  cross  section,  and  then  treating  as  a 
new  specimen,  it  was  tested  for  elastic  limit,  modulus  and 
ultimate.  The  reduction  given  is  the  total  reduction.  The 
modulus  is  about  the  same  for  both  tests.  The  object  of  this 
test  was  to  determine  if,  in  case  one  part  of  a  bar  of  this  grade 
of  steel  should  receive  a  greater  stress  than  the  other  parts,  even 
to  causing  it  to  pass  the  elastic  limit,  its  modulus  would  still 
enable  it  to  resist  in  proportion  to  its  section  as  much  as  before. 
If  its  modulus  is  not  altered  by  stretching,  the  structure  of 
which  it  formed  a  part  might  not  be  immediately  rendered 
unsafe,  but  it  is  more  a  matter  of  curiosity  than  otherwise  as 
nobody  would  think  of  straining  material  to  that  extent. 

From  a  study  of  the  tests  of  steel  it  appears  that  below  the 
elastic  limit,  for  a  direct  tensile  stress,  a  slight  nick  would  not 
be  dangerous,  but  that  the  danger  from  the  nick  lies  more  in 
having  transverse  vibrations  take  pla^e  which,  concentrating  a 
heavy  stress  at  the  bottom  of  the  nick,  would  cause  it  to  break- 

The  tensive  strain  that  was  on  the  specimens  at  the  time  of 
striking  them  was  no  doubt  an  assistance  in  preventing  trans* 
verse  vibration  in  the  bar,  causing  it  to  resist  the  effect  of  the 
blow,  where  the  same  blow  would  have  broken  it  without  the 
tension. 

The  modulus  of  steel,  being  so  much  less  than  that  of  iron 
in  proportion  to  their  elastic  limitc,  gives  to  the  trusses  greater 
flexibility  for  the  same  depth  of  truss  when  made  of  steel  than 
if  made  of  iron.  L.  L.  BUCK. 


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SUSPENSION  BRIDGE. 


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100^*^* 200 300 


400 


■^IS^g^JUJg^ 


Fi,.  I. 


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Plate  VI . 


^US8  yirttl/Q  c^-r-g 


CM 

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I 


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5 


500 


M 

I 


600- 


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3 

I 


700 


I 


900 


